xen: add support for PAT
Convert Linux PAT entries into Xen ones when constructing ptes. Linux
doesn't use _PAGE_PAT for ptes, so the only difference in the first 4
entries is that Linux uses _PAGE_PWT for WC, whereas Xen (and default)
use it for WT.
xen_pte_val does the inverse conversion.
We hard-code assumptions about Linux's current PAT layout, but a
warning on the wrmsr to MSR_IA32_CR_PAT should point out any problems.
If necessary we could go to a more general table-based conversion between
Linux and Xen PAT entries.
hugetlbfs poses a problem at the moment, the x86 architecture uses the
same flag for _PAGE_PAT and _PAGE_PSE, which changes meaning depending
on which pagetable level we're using. At the moment this should be OK
so long as nobody tries to do a pte_val on a hugetlbfs pte.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index b237167..67b4101 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -55,6 +55,7 @@
#include <asm/e820.h>
#include <asm/linkage.h>
#include <asm/page.h>
+#include <asm/pat.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>
@@ -780,10 +781,18 @@
pteval_t xen_pte_val(pte_t pte)
{
- if (xen_initial_domain() && (pte.pte & _PAGE_IOMAP))
- return pte.pte;
+ pteval_t pteval = pte.pte;
- return pte_mfn_to_pfn(pte.pte);
+ /* If this is a WC pte, convert back from Xen WC to Linux WC */
+ if ((pteval & (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)) == _PAGE_PAT) {
+ WARN_ON(!pat_enabled);
+ pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;
+ }
+
+ if (xen_initial_domain() && (pteval & _PAGE_IOMAP))
+ return pteval;
+
+ return pte_mfn_to_pfn(pteval);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);
@@ -793,10 +802,48 @@
}
PV_CALLEE_SAVE_REGS_THUNK(xen_pgd_val);
+/*
+ * Xen's PAT setup is part of its ABI, though I assume entries 6 & 7
+ * are reserved for now, to correspond to the Intel-reserved PAT
+ * types.
+ *
+ * We expect Linux's PAT set as follows:
+ *
+ * Idx PTE flags Linux Xen Default
+ * 0 WB WB WB
+ * 1 PWT WC WT WT
+ * 2 PCD UC- UC- UC-
+ * 3 PCD PWT UC UC UC
+ * 4 PAT WB WC WB
+ * 5 PAT PWT WC WP WT
+ * 6 PAT PCD UC- UC UC-
+ * 7 PAT PCD PWT UC UC UC
+ */
+
+void xen_set_pat(u64 pat)
+{
+ /* We expect Linux to use a PAT setting of
+ * UC UC- WC WB (ignoring the PAT flag) */
+ WARN_ON(pat != 0x0007010600070106ull);
+}
+
pte_t xen_make_pte(pteval_t pte)
{
phys_addr_t addr = (pte & PTE_PFN_MASK);
+ /* If Linux is trying to set a WC pte, then map to the Xen WC.
+ * If _PAGE_PAT is set, then it probably means it is really
+ * _PAGE_PSE, so avoid fiddling with the PAT mapping and hope
+ * things work out OK...
+ *
+ * (We should never see kernel mappings with _PAGE_PSE set,
+ * but we could see hugetlbfs mappings, I think.).
+ */
+ if (pat_enabled && !WARN_ON(pte & _PAGE_PAT)) {
+ if ((pte & (_PAGE_PCD | _PAGE_PWT)) == _PAGE_PWT)
+ pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT;
+ }
+
/*
* Unprivileged domains are allowed to do IOMAPpings for
* PCI passthrough, but not map ISA space. The ISA