| /*P:700 The pagetable code, on the other hand, still shows the scars of |
| * previous encounters. It's functional, and as neat as it can be in the |
| * circumstances, but be wary, for these things are subtle and break easily. |
| * The Guest provides a virtual to physical mapping, but we can neither trust |
| * it nor use it: we verify and convert it here to point the hardware to the |
| * actual Guest pages when running the Guest. :*/ |
| |
| /* Copyright (C) Rusty Russell IBM Corporation 2006. |
| * GPL v2 and any later version */ |
| #include <linux/mm.h> |
| #include <linux/types.h> |
| #include <linux/spinlock.h> |
| #include <linux/random.h> |
| #include <linux/percpu.h> |
| #include <asm/tlbflush.h> |
| #include "lg.h" |
| |
| /*M:008 We hold reference to pages, which prevents them from being swapped. |
| * It'd be nice to have a callback in the "struct mm_struct" when Linux wants |
| * to swap out. If we had this, and a shrinker callback to trim PTE pages, we |
| * could probably consider launching Guests as non-root. :*/ |
| |
| /*H:300 |
| * The Page Table Code |
| * |
| * We use two-level page tables for the Guest. If you're not entirely |
| * comfortable with virtual addresses, physical addresses and page tables then |
| * I recommend you review lguest.c's "Page Table Handling" (with diagrams!). |
| * |
| * The Guest keeps page tables, but we maintain the actual ones here: these are |
| * called "shadow" page tables. Which is a very Guest-centric name: these are |
| * the real page tables the CPU uses, although we keep them up to date to |
| * reflect the Guest's. (See what I mean about weird naming? Since when do |
| * shadows reflect anything?) |
| * |
| * Anyway, this is the most complicated part of the Host code. There are seven |
| * parts to this: |
| * (i) Setting up a page table entry for the Guest when it faults, |
| * (ii) Setting up the page table entry for the Guest stack, |
| * (iii) Setting up a page table entry when the Guest tells us it has changed, |
| * (iv) Switching page tables, |
| * (v) Flushing (thowing away) page tables, |
| * (vi) Mapping the Switcher when the Guest is about to run, |
| * (vii) Setting up the page tables initially. |
| :*/ |
| |
| /* Pages a 4k long, and each page table entry is 4 bytes long, giving us 1024 |
| * (or 2^10) entries per page. */ |
| #define PTES_PER_PAGE_SHIFT 10 |
| #define PTES_PER_PAGE (1 << PTES_PER_PAGE_SHIFT) |
| |
| /* 1024 entries in a page table page maps 1024 pages: 4MB. The Switcher is |
| * conveniently placed at the top 4MB, so it uses a separate, complete PTE |
| * page. */ |
| #define SWITCHER_PGD_INDEX (PTES_PER_PAGE - 1) |
| |
| /* We actually need a separate PTE page for each CPU. Remember that after the |
| * Switcher code itself comes two pages for each CPU, and we don't want this |
| * CPU's guest to see the pages of any other CPU. */ |
| static DEFINE_PER_CPU(spte_t *, switcher_pte_pages); |
| #define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu) |
| |
| /*H:320 With our shadow and Guest types established, we need to deal with |
| * them: the page table code is curly enough to need helper functions to keep |
| * it clear and clean. |
| * |
| * The first helper takes a virtual address, and says which entry in the top |
| * level page table deals with that address. Since each top level entry deals |
| * with 4M, this effectively divides by 4M. */ |
| static unsigned vaddr_to_pgd_index(unsigned long vaddr) |
| { |
| return vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT); |
| } |
| |
| /* There are two functions which return pointers to the shadow (aka "real") |
| * page tables. |
| * |
| * spgd_addr() takes the virtual address and returns a pointer to the top-level |
| * page directory entry for that address. Since we keep track of several page |
| * tables, the "i" argument tells us which one we're interested in (it's |
| * usually the current one). */ |
| static spgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr) |
| { |
| unsigned int index = vaddr_to_pgd_index(vaddr); |
| |
| /* We kill any Guest trying to touch the Switcher addresses. */ |
| if (index >= SWITCHER_PGD_INDEX) { |
| kill_guest(lg, "attempt to access switcher pages"); |
| index = 0; |
| } |
| /* Return a pointer index'th pgd entry for the i'th page table. */ |
| return &lg->pgdirs[i].pgdir[index]; |
| } |
| |
| /* This routine then takes the PGD entry given above, which contains the |
| * address of the PTE page. It then returns a pointer to the PTE entry for the |
| * given address. */ |
| static spte_t *spte_addr(struct lguest *lg, spgd_t spgd, unsigned long vaddr) |
| { |
| spte_t *page = __va(spgd.pfn << PAGE_SHIFT); |
| /* You should never call this if the PGD entry wasn't valid */ |
| BUG_ON(!(spgd.flags & _PAGE_PRESENT)); |
| return &page[(vaddr >> PAGE_SHIFT) % PTES_PER_PAGE]; |
| } |
| |
| /* These two functions just like the above two, except they access the Guest |
| * page tables. Hence they return a Guest address. */ |
| static unsigned long gpgd_addr(struct lguest *lg, unsigned long vaddr) |
| { |
| unsigned int index = vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT); |
| return lg->pgdirs[lg->pgdidx].cr3 + index * sizeof(gpgd_t); |
| } |
| |
| static unsigned long gpte_addr(struct lguest *lg, |
| gpgd_t gpgd, unsigned long vaddr) |
| { |
| unsigned long gpage = gpgd.pfn << PAGE_SHIFT; |
| BUG_ON(!(gpgd.flags & _PAGE_PRESENT)); |
| return gpage + ((vaddr>>PAGE_SHIFT) % PTES_PER_PAGE) * sizeof(gpte_t); |
| } |
| |
| /*H:350 This routine takes a page number given by the Guest and converts it to |
| * an actual, physical page number. It can fail for several reasons: the |
| * virtual address might not be mapped by the Launcher, the write flag is set |
| * and the page is read-only, or the write flag was set and the page was |
| * shared so had to be copied, but we ran out of memory. |
| * |
| * This holds a reference to the page, so release_pte() is careful to |
| * put that back. */ |
| static unsigned long get_pfn(unsigned long virtpfn, int write) |
| { |
| struct page *page; |
| /* This value indicates failure. */ |
| unsigned long ret = -1UL; |
| |
| /* get_user_pages() is a complex interface: it gets the "struct |
| * vm_area_struct" and "struct page" assocated with a range of pages. |
| * It also needs the task's mmap_sem held, and is not very quick. |
| * It returns the number of pages it got. */ |
| down_read(¤t->mm->mmap_sem); |
| if (get_user_pages(current, current->mm, virtpfn << PAGE_SHIFT, |
| 1, write, 1, &page, NULL) == 1) |
| ret = page_to_pfn(page); |
| up_read(¤t->mm->mmap_sem); |
| return ret; |
| } |
| |
| /*H:340 Converting a Guest page table entry to a shadow (ie. real) page table |
| * entry can be a little tricky. The flags are (almost) the same, but the |
| * Guest PTE contains a virtual page number: the CPU needs the real page |
| * number. */ |
| static spte_t gpte_to_spte(struct lguest *lg, gpte_t gpte, int write) |
| { |
| spte_t spte; |
| unsigned long pfn, base; |
| |
| /* The Guest sets the global flag, because it thinks that it is using |
| * PGE. We only told it to use PGE so it would tell us whether it was |
| * flushing a kernel mapping or a userspace mapping. We don't actually |
| * use the global bit, so throw it away. */ |
| spte.flags = (gpte.flags & ~_PAGE_GLOBAL); |
| |
| /* The Guest's pages are offset inside the Launcher. */ |
| base = (unsigned long)lg->mem_base / PAGE_SIZE; |
| |
| /* We need a temporary "unsigned long" variable to hold the answer from |
| * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't |
| * fit in spte.pfn. get_pfn() finds the real physical number of the |
| * page, given the virtual number. */ |
| pfn = get_pfn(base + gpte.pfn, write); |
| if (pfn == -1UL) { |
| kill_guest(lg, "failed to get page %u", gpte.pfn); |
| /* When we destroy the Guest, we'll go through the shadow page |
| * tables and release_pte() them. Make sure we don't think |
| * this one is valid! */ |
| spte.flags = 0; |
| } |
| /* Now we assign the page number, and our shadow PTE is complete. */ |
| spte.pfn = pfn; |
| return spte; |
| } |
| |
| /*H:460 And to complete the chain, release_pte() looks like this: */ |
| static void release_pte(spte_t pte) |
| { |
| /* Remember that get_user_pages() took a reference to the page, in |
| * get_pfn()? We have to put it back now. */ |
| if (pte.flags & _PAGE_PRESENT) |
| put_page(pfn_to_page(pte.pfn)); |
| } |
| /*:*/ |
| |
| static void check_gpte(struct lguest *lg, gpte_t gpte) |
| { |
| if ((gpte.flags & (_PAGE_PWT|_PAGE_PSE)) || gpte.pfn >= lg->pfn_limit) |
| kill_guest(lg, "bad page table entry"); |
| } |
| |
| static void check_gpgd(struct lguest *lg, gpgd_t gpgd) |
| { |
| if ((gpgd.flags & ~_PAGE_TABLE) || gpgd.pfn >= lg->pfn_limit) |
| kill_guest(lg, "bad page directory entry"); |
| } |
| |
| /*H:330 |
| * (i) Setting up a page table entry for the Guest when it faults |
| * |
| * We saw this call in run_guest(): when we see a page fault in the Guest, we |
| * come here. That's because we only set up the shadow page tables lazily as |
| * they're needed, so we get page faults all the time and quietly fix them up |
| * and return to the Guest without it knowing. |
| * |
| * If we fixed up the fault (ie. we mapped the address), this routine returns |
| * true. */ |
| int demand_page(struct lguest *lg, unsigned long vaddr, int errcode) |
| { |
| gpgd_t gpgd; |
| spgd_t *spgd; |
| unsigned long gpte_ptr; |
| gpte_t gpte; |
| spte_t *spte; |
| |
| /* First step: get the top-level Guest page table entry. */ |
| gpgd = mkgpgd(lgread_u32(lg, gpgd_addr(lg, vaddr))); |
| /* Toplevel not present? We can't map it in. */ |
| if (!(gpgd.flags & _PAGE_PRESENT)) |
| return 0; |
| |
| /* Now look at the matching shadow entry. */ |
| spgd = spgd_addr(lg, lg->pgdidx, vaddr); |
| if (!(spgd->flags & _PAGE_PRESENT)) { |
| /* No shadow entry: allocate a new shadow PTE page. */ |
| unsigned long ptepage = get_zeroed_page(GFP_KERNEL); |
| /* This is not really the Guest's fault, but killing it is |
| * simple for this corner case. */ |
| if (!ptepage) { |
| kill_guest(lg, "out of memory allocating pte page"); |
| return 0; |
| } |
| /* We check that the Guest pgd is OK. */ |
| check_gpgd(lg, gpgd); |
| /* And we copy the flags to the shadow PGD entry. The page |
| * number in the shadow PGD is the page we just allocated. */ |
| spgd->raw.val = (__pa(ptepage) | gpgd.flags); |
| } |
| |
| /* OK, now we look at the lower level in the Guest page table: keep its |
| * address, because we might update it later. */ |
| gpte_ptr = gpte_addr(lg, gpgd, vaddr); |
| gpte = mkgpte(lgread_u32(lg, gpte_ptr)); |
| |
| /* If this page isn't in the Guest page tables, we can't page it in. */ |
| if (!(gpte.flags & _PAGE_PRESENT)) |
| return 0; |
| |
| /* Check they're not trying to write to a page the Guest wants |
| * read-only (bit 2 of errcode == write). */ |
| if ((errcode & 2) && !(gpte.flags & _PAGE_RW)) |
| return 0; |
| |
| /* User access to a kernel page? (bit 3 == user access) */ |
| if ((errcode & 4) && !(gpte.flags & _PAGE_USER)) |
| return 0; |
| |
| /* Check that the Guest PTE flags are OK, and the page number is below |
| * the pfn_limit (ie. not mapping the Launcher binary). */ |
| check_gpte(lg, gpte); |
| /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */ |
| gpte.flags |= _PAGE_ACCESSED; |
| if (errcode & 2) |
| gpte.flags |= _PAGE_DIRTY; |
| |
| /* Get the pointer to the shadow PTE entry we're going to set. */ |
| spte = spte_addr(lg, *spgd, vaddr); |
| /* If there was a valid shadow PTE entry here before, we release it. |
| * This can happen with a write to a previously read-only entry. */ |
| release_pte(*spte); |
| |
| /* If this is a write, we insist that the Guest page is writable (the |
| * final arg to gpte_to_spte()). */ |
| if (gpte.flags & _PAGE_DIRTY) |
| *spte = gpte_to_spte(lg, gpte, 1); |
| else { |
| /* If this is a read, don't set the "writable" bit in the page |
| * table entry, even if the Guest says it's writable. That way |
| * we come back here when a write does actually ocur, so we can |
| * update the Guest's _PAGE_DIRTY flag. */ |
| gpte_t ro_gpte = gpte; |
| ro_gpte.flags &= ~_PAGE_RW; |
| *spte = gpte_to_spte(lg, ro_gpte, 0); |
| } |
| |
| /* Finally, we write the Guest PTE entry back: we've set the |
| * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */ |
| lgwrite_u32(lg, gpte_ptr, gpte.raw.val); |
| |
| /* We succeeded in mapping the page! */ |
| return 1; |
| } |
| |
| /*H:360 (ii) Setting up the page table entry for the Guest stack. |
| * |
| * Remember pin_stack_pages() which makes sure the stack is mapped? It could |
| * simply call demand_page(), but as we've seen that logic is quite long, and |
| * usually the stack pages are already mapped anyway, so it's not required. |
| * |
| * This is a quick version which answers the question: is this virtual address |
| * mapped by the shadow page tables, and is it writable? */ |
| static int page_writable(struct lguest *lg, unsigned long vaddr) |
| { |
| spgd_t *spgd; |
| unsigned long flags; |
| |
| /* Look at the top level entry: is it present? */ |
| spgd = spgd_addr(lg, lg->pgdidx, vaddr); |
| if (!(spgd->flags & _PAGE_PRESENT)) |
| return 0; |
| |
| /* Check the flags on the pte entry itself: it must be present and |
| * writable. */ |
| flags = spte_addr(lg, *spgd, vaddr)->flags; |
| return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW); |
| } |
| |
| /* So, when pin_stack_pages() asks us to pin a page, we check if it's already |
| * in the page tables, and if not, we call demand_page() with error code 2 |
| * (meaning "write"). */ |
| void pin_page(struct lguest *lg, unsigned long vaddr) |
| { |
| if (!page_writable(lg, vaddr) && !demand_page(lg, vaddr, 2)) |
| kill_guest(lg, "bad stack page %#lx", vaddr); |
| } |
| |
| /*H:450 If we chase down the release_pgd() code, it looks like this: */ |
| static void release_pgd(struct lguest *lg, spgd_t *spgd) |
| { |
| /* If the entry's not present, there's nothing to release. */ |
| if (spgd->flags & _PAGE_PRESENT) { |
| unsigned int i; |
| /* Converting the pfn to find the actual PTE page is easy: turn |
| * the page number into a physical address, then convert to a |
| * virtual address (easy for kernel pages like this one). */ |
| spte_t *ptepage = __va(spgd->pfn << PAGE_SHIFT); |
| /* For each entry in the page, we might need to release it. */ |
| for (i = 0; i < PTES_PER_PAGE; i++) |
| release_pte(ptepage[i]); |
| /* Now we can free the page of PTEs */ |
| free_page((long)ptepage); |
| /* And zero out the PGD entry we we never release it twice. */ |
| spgd->raw.val = 0; |
| } |
| } |
| |
| /*H:440 (v) Flushing (thowing away) page tables, |
| * |
| * We saw flush_user_mappings() called when we re-used a top-level pgdir page. |
| * It simply releases every PTE page from 0 up to the kernel address. */ |
| static void flush_user_mappings(struct lguest *lg, int idx) |
| { |
| unsigned int i; |
| /* Release every pgd entry up to the kernel's address. */ |
| for (i = 0; i < vaddr_to_pgd_index(lg->page_offset); i++) |
| release_pgd(lg, lg->pgdirs[idx].pgdir + i); |
| } |
| |
| /* The Guest also has a hypercall to do this manually: it's used when a large |
| * number of mappings have been changed. */ |
| void guest_pagetable_flush_user(struct lguest *lg) |
| { |
| /* Drop the userspace part of the current page table. */ |
| flush_user_mappings(lg, lg->pgdidx); |
| } |
| /*:*/ |
| |
| /* We keep several page tables. This is a simple routine to find the page |
| * table (if any) corresponding to this top-level address the Guest has given |
| * us. */ |
| static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable) |
| { |
| unsigned int i; |
| for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) |
| if (lg->pgdirs[i].cr3 == pgtable) |
| break; |
| return i; |
| } |
| |
| /*H:435 And this is us, creating the new page directory. If we really do |
| * allocate a new one (and so the kernel parts are not there), we set |
| * blank_pgdir. */ |
| static unsigned int new_pgdir(struct lguest *lg, |
| unsigned long cr3, |
| int *blank_pgdir) |
| { |
| unsigned int next; |
| |
| /* We pick one entry at random to throw out. Choosing the Least |
| * Recently Used might be better, but this is easy. */ |
| next = random32() % ARRAY_SIZE(lg->pgdirs); |
| /* If it's never been allocated at all before, try now. */ |
| if (!lg->pgdirs[next].pgdir) { |
| lg->pgdirs[next].pgdir = (spgd_t *)get_zeroed_page(GFP_KERNEL); |
| /* If the allocation fails, just keep using the one we have */ |
| if (!lg->pgdirs[next].pgdir) |
| next = lg->pgdidx; |
| else |
| /* This is a blank page, so there are no kernel |
| * mappings: caller must map the stack! */ |
| *blank_pgdir = 1; |
| } |
| /* Record which Guest toplevel this shadows. */ |
| lg->pgdirs[next].cr3 = cr3; |
| /* Release all the non-kernel mappings. */ |
| flush_user_mappings(lg, next); |
| |
| return next; |
| } |
| |
| /*H:430 (iv) Switching page tables |
| * |
| * This is what happens when the Guest changes page tables (ie. changes the |
| * top-level pgdir). This happens on almost every context switch. */ |
| void guest_new_pagetable(struct lguest *lg, unsigned long pgtable) |
| { |
| int newpgdir, repin = 0; |
| |
| /* Look to see if we have this one already. */ |
| newpgdir = find_pgdir(lg, pgtable); |
| /* If not, we allocate or mug an existing one: if it's a fresh one, |
| * repin gets set to 1. */ |
| if (newpgdir == ARRAY_SIZE(lg->pgdirs)) |
| newpgdir = new_pgdir(lg, pgtable, &repin); |
| /* Change the current pgd index to the new one. */ |
| lg->pgdidx = newpgdir; |
| /* If it was completely blank, we map in the Guest kernel stack */ |
| if (repin) |
| pin_stack_pages(lg); |
| } |
| |
| /*H:470 Finally, a routine which throws away everything: all PGD entries in all |
| * the shadow page tables. This is used when we destroy the Guest. */ |
| static void release_all_pagetables(struct lguest *lg) |
| { |
| unsigned int i, j; |
| |
| /* Every shadow pagetable this Guest has */ |
| for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) |
| if (lg->pgdirs[i].pgdir) |
| /* Every PGD entry except the Switcher at the top */ |
| for (j = 0; j < SWITCHER_PGD_INDEX; j++) |
| release_pgd(lg, lg->pgdirs[i].pgdir + j); |
| } |
| |
| /* We also throw away everything when a Guest tells us it's changed a kernel |
| * mapping. Since kernel mappings are in every page table, it's easiest to |
| * throw them all away. This is amazingly slow, but thankfully rare. */ |
| void guest_pagetable_clear_all(struct lguest *lg) |
| { |
| release_all_pagetables(lg); |
| /* We need the Guest kernel stack mapped again. */ |
| pin_stack_pages(lg); |
| } |
| |
| /*H:420 This is the routine which actually sets the page table entry for then |
| * "idx"'th shadow page table. |
| * |
| * Normally, we can just throw out the old entry and replace it with 0: if they |
| * use it demand_page() will put the new entry in. We need to do this anyway: |
| * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page |
| * is read from, and _PAGE_DIRTY when it's written to. |
| * |
| * But Avi Kivity pointed out that most Operating Systems (Linux included) set |
| * these bits on PTEs immediately anyway. This is done to save the CPU from |
| * having to update them, but it helps us the same way: if they set |
| * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if |
| * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately. |
| */ |
| static void do_set_pte(struct lguest *lg, int idx, |
| unsigned long vaddr, gpte_t gpte) |
| { |
| /* Look up the matching shadow page directot entry. */ |
| spgd_t *spgd = spgd_addr(lg, idx, vaddr); |
| |
| /* If the top level isn't present, there's no entry to update. */ |
| if (spgd->flags & _PAGE_PRESENT) { |
| /* Otherwise, we start by releasing the existing entry. */ |
| spte_t *spte = spte_addr(lg, *spgd, vaddr); |
| release_pte(*spte); |
| |
| /* If they're setting this entry as dirty or accessed, we might |
| * as well put that entry they've given us in now. This shaves |
| * 10% off a copy-on-write micro-benchmark. */ |
| if (gpte.flags & (_PAGE_DIRTY | _PAGE_ACCESSED)) { |
| check_gpte(lg, gpte); |
| *spte = gpte_to_spte(lg, gpte, gpte.flags&_PAGE_DIRTY); |
| } else |
| /* Otherwise we can demand_page() it in later. */ |
| spte->raw.val = 0; |
| } |
| } |
| |
| /*H:410 Updating a PTE entry is a little trickier. |
| * |
| * We keep track of several different page tables (the Guest uses one for each |
| * process, so it makes sense to cache at least a few). Each of these have |
| * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for |
| * all processes. So when the page table above that address changes, we update |
| * all the page tables, not just the current one. This is rare. |
| * |
| * The benefit is that when we have to track a new page table, we can copy keep |
| * all the kernel mappings. This speeds up context switch immensely. */ |
| void guest_set_pte(struct lguest *lg, |
| unsigned long cr3, unsigned long vaddr, gpte_t gpte) |
| { |
| /* Kernel mappings must be changed on all top levels. Slow, but |
| * doesn't happen often. */ |
| if (vaddr >= lg->page_offset) { |
| unsigned int i; |
| for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) |
| if (lg->pgdirs[i].pgdir) |
| do_set_pte(lg, i, vaddr, gpte); |
| } else { |
| /* Is this page table one we have a shadow for? */ |
| int pgdir = find_pgdir(lg, cr3); |
| if (pgdir != ARRAY_SIZE(lg->pgdirs)) |
| /* If so, do the update. */ |
| do_set_pte(lg, pgdir, vaddr, gpte); |
| } |
| } |
| |
| /*H:400 |
| * (iii) Setting up a page table entry when the Guest tells us it has changed. |
| * |
| * Just like we did in interrupts_and_traps.c, it makes sense for us to deal |
| * with the other side of page tables while we're here: what happens when the |
| * Guest asks for a page table to be updated? |
| * |
| * We already saw that demand_page() will fill in the shadow page tables when |
| * needed, so we can simply remove shadow page table entries whenever the Guest |
| * tells us they've changed. When the Guest tries to use the new entry it will |
| * fault and demand_page() will fix it up. |
| * |
| * So with that in mind here's our code to to update a (top-level) PGD entry: |
| */ |
| void guest_set_pmd(struct lguest *lg, unsigned long cr3, u32 idx) |
| { |
| int pgdir; |
| |
| /* The kernel seems to try to initialize this early on: we ignore its |
| * attempts to map over the Switcher. */ |
| if (idx >= SWITCHER_PGD_INDEX) |
| return; |
| |
| /* If they're talking about a page table we have a shadow for... */ |
| pgdir = find_pgdir(lg, cr3); |
| if (pgdir < ARRAY_SIZE(lg->pgdirs)) |
| /* ... throw it away. */ |
| release_pgd(lg, lg->pgdirs[pgdir].pgdir + idx); |
| } |
| |
| /*H:500 (vii) Setting up the page tables initially. |
| * |
| * When a Guest is first created, the Launcher tells us where the toplevel of |
| * its first page table is. We set some things up here: */ |
| int init_guest_pagetable(struct lguest *lg, unsigned long pgtable) |
| { |
| /* In flush_user_mappings() we loop from 0 to |
| * "vaddr_to_pgd_index(lg->page_offset)". This assumes it won't hit |
| * the Switcher mappings, so check that now. */ |
| if (vaddr_to_pgd_index(lg->page_offset) >= SWITCHER_PGD_INDEX) |
| return -EINVAL; |
| /* We start on the first shadow page table, and give it a blank PGD |
| * page. */ |
| lg->pgdidx = 0; |
| lg->pgdirs[lg->pgdidx].cr3 = pgtable; |
| lg->pgdirs[lg->pgdidx].pgdir = (spgd_t*)get_zeroed_page(GFP_KERNEL); |
| if (!lg->pgdirs[lg->pgdidx].pgdir) |
| return -ENOMEM; |
| return 0; |
| } |
| |
| /* When a Guest dies, our cleanup is fairly simple. */ |
| void free_guest_pagetable(struct lguest *lg) |
| { |
| unsigned int i; |
| |
| /* Throw away all page table pages. */ |
| release_all_pagetables(lg); |
| /* Now free the top levels: free_page() can handle 0 just fine. */ |
| for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) |
| free_page((long)lg->pgdirs[i].pgdir); |
| } |
| |
| /*H:480 (vi) Mapping the Switcher when the Guest is about to run. |
| * |
| * The Switcher and the two pages for this CPU need to be available to the |
| * Guest (and not the pages for other CPUs). We have the appropriate PTE pages |
| * for each CPU already set up, we just need to hook them in. */ |
| void map_switcher_in_guest(struct lguest *lg, struct lguest_pages *pages) |
| { |
| spte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages); |
| spgd_t switcher_pgd; |
| spte_t regs_pte; |
| |
| /* Make the last PGD entry for this Guest point to the Switcher's PTE |
| * page for this CPU (with appropriate flags). */ |
| switcher_pgd.pfn = __pa(switcher_pte_page) >> PAGE_SHIFT; |
| switcher_pgd.flags = _PAGE_KERNEL; |
| lg->pgdirs[lg->pgdidx].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd; |
| |
| /* We also change the Switcher PTE page. When we're running the Guest, |
| * we want the Guest's "regs" page to appear where the first Switcher |
| * page for this CPU is. This is an optimization: when the Switcher |
| * saves the Guest registers, it saves them into the first page of this |
| * CPU's "struct lguest_pages": if we make sure the Guest's register |
| * page is already mapped there, we don't have to copy them out |
| * again. */ |
| regs_pte.pfn = __pa(lg->regs_page) >> PAGE_SHIFT; |
| regs_pte.flags = _PAGE_KERNEL; |
| switcher_pte_page[(unsigned long)pages/PAGE_SIZE%PTES_PER_PAGE] |
| = regs_pte; |
| } |
| /*:*/ |
| |
| static void free_switcher_pte_pages(void) |
| { |
| unsigned int i; |
| |
| for_each_possible_cpu(i) |
| free_page((long)switcher_pte_page(i)); |
| } |
| |
| /*H:520 Setting up the Switcher PTE page for given CPU is fairly easy, given |
| * the CPU number and the "struct page"s for the Switcher code itself. |
| * |
| * Currently the Switcher is less than a page long, so "pages" is always 1. */ |
| static __init void populate_switcher_pte_page(unsigned int cpu, |
| struct page *switcher_page[], |
| unsigned int pages) |
| { |
| unsigned int i; |
| spte_t *pte = switcher_pte_page(cpu); |
| |
| /* The first entries are easy: they map the Switcher code. */ |
| for (i = 0; i < pages; i++) { |
| pte[i].pfn = page_to_pfn(switcher_page[i]); |
| pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED; |
| } |
| |
| /* The only other thing we map is this CPU's pair of pages. */ |
| i = pages + cpu*2; |
| |
| /* First page (Guest registers) is writable from the Guest */ |
| pte[i].pfn = page_to_pfn(switcher_page[i]); |
| pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW; |
| /* The second page contains the "struct lguest_ro_state", and is |
| * read-only. */ |
| pte[i+1].pfn = page_to_pfn(switcher_page[i+1]); |
| pte[i+1].flags = _PAGE_PRESENT|_PAGE_ACCESSED; |
| } |
| |
| /*H:510 At boot or module load time, init_pagetables() allocates and populates |
| * the Switcher PTE page for each CPU. */ |
| __init int init_pagetables(struct page **switcher_page, unsigned int pages) |
| { |
| unsigned int i; |
| |
| for_each_possible_cpu(i) { |
| switcher_pte_page(i) = (spte_t *)get_zeroed_page(GFP_KERNEL); |
| if (!switcher_pte_page(i)) { |
| free_switcher_pte_pages(); |
| return -ENOMEM; |
| } |
| populate_switcher_pte_page(i, switcher_page, pages); |
| } |
| return 0; |
| } |
| /*:*/ |
| |
| /* Cleaning up simply involves freeing the PTE page for each CPU. */ |
| void free_pagetables(void) |
| { |
| free_switcher_pte_pages(); |
| } |