lguest: support backdoor window.
The VIRTIO_PCI_CAP_PCI_CFG in the PCI virtio 1.0 spec allows access to
the BAR registers without mapping them. This is a compulsory feature,
and we implement it here.
There are some subtleties involving access widths which we should
note:
4.1.4.7.1 Device Requirements: PCI configuration access capability
...
Upon detecting driver write access to pci_cfg_data, the device MUST
execute a write access at offset cap.offset at BAR selected by
cap.bar using the first cap.length bytes from pci_cfg_data.
Upon detecting driver read access to pci_cfg_data, the device MUST
execute a read access of length cap.length at offset cap.offset at
BAR selected by cap.bar and store the first cap.length bytes in
pci_cfg_data.
So, for a write, we copy into the pci_cfg_data window, then write from
there out to the BAR. This works correctly if cap.length != width of
write. Similarly, for a read, we read into window from the BAR then
read the value from there.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/tools/lguest/lguest.c b/tools/lguest/lguest.c
index 8959ac2..e3c4d3d 100644
--- a/tools/lguest/lguest.c
+++ b/tools/lguest/lguest.c
@@ -156,7 +156,6 @@
struct virtio_pci_notify_cap notify;
struct virtio_pci_cap isr;
struct virtio_pci_cap device;
- /* FIXME: Implement this! */
struct virtio_pci_cfg_cap cfg_access;
};
@@ -1184,6 +1183,36 @@
return find_pci_device(pci_config_addr.bits.devnum);
}
+/*
+ * We can get invalid combinations of values while they're writing, so we
+ * only fault if they try to write with some invalid bar/offset/length.
+ */
+static bool valid_bar_access(struct device *d,
+ struct virtio_pci_cfg_cap *cfg_access)
+{
+ /* We only have 1 bar (BAR0) */
+ if (cfg_access->cap.bar != 0)
+ return false;
+
+ /* Check it's within BAR0. */
+ if (cfg_access->cap.offset >= d->mmio_size
+ || cfg_access->cap.offset + cfg_access->cap.length > d->mmio_size)
+ return false;
+
+ /* Check length is 1, 2 or 4. */
+ if (cfg_access->cap.length != 1
+ && cfg_access->cap.length != 2
+ && cfg_access->cap.length != 4)
+ return false;
+
+ /* Offset must be multiple of length */
+ if (cfg_access->cap.offset % cfg_access->cap.length != 0)
+ return false;
+
+ /* Return pointer into word in BAR0. */
+ return true;
+}
+
/* Is this accessing the PCI config address port?. */
static bool is_pci_addr_port(u16 port)
{
@@ -1215,6 +1244,8 @@
return port >= PCI_CONFIG_DATA && port < PCI_CONFIG_DATA + 4;
}
+static void emulate_mmio_write(struct device *d, u32 off, u32 val, u32 mask);
+
static bool pci_data_iowrite(u16 port, u32 mask, u32 val)
{
u32 reg, portoff;
@@ -1255,12 +1286,53 @@
&& mask == 0xFFFF) {
/* Ignore command writes. */
return true;
+ } else if (&d->config_words[reg]
+ == (void *)&d->config.cfg_access.cap.bar
+ || &d->config_words[reg]
+ == &d->config.cfg_access.cap.length
+ || &d->config_words[reg]
+ == &d->config.cfg_access.cap.offset) {
+
+ /*
+ * The VIRTIO_PCI_CAP_PCI_CFG capability
+ * provides a backdoor to access the MMIO
+ * regions without mapping them. Weird, but
+ * useful.
+ */
+ iowrite(portoff, val, mask, &d->config_words[reg]);
+ return true;
+ } else if (&d->config_words[reg] == &d->config.cfg_access.window) {
+ u32 write_mask;
+
+ /* Must be bar 0 */
+ if (!valid_bar_access(d, &d->config.cfg_access))
+ return false;
+
+ /* First copy what they wrote into the window */
+ iowrite(portoff, val, mask, &d->config.cfg_access.window);
+
+ /*
+ * Now emulate a write. The mask we use is set by
+ * len, *not* this write!
+ */
+ write_mask = (1ULL<<(8*d->config.cfg_access.cap.length)) - 1;
+ verbose("Window writing %#x/%#x to bar %u, offset %u len %u\n",
+ d->config.cfg_access.window, write_mask,
+ d->config.cfg_access.cap.bar,
+ d->config.cfg_access.cap.offset,
+ d->config.cfg_access.cap.length);
+
+ emulate_mmio_write(d, d->config.cfg_access.cap.offset,
+ d->config.cfg_access.window, write_mask);
+ return true;
}
/* Complain about other writes. */
return false;
}
+static u32 emulate_mmio_read(struct device *d, u32 off, u32 mask);
+
static void pci_data_ioread(u16 port, u32 mask, u32 *val)
{
u32 reg;
@@ -1268,6 +1340,33 @@
if (!d)
return;
+
+ /* Read through the PCI MMIO access window is special */
+ if (&d->config_words[reg] == &d->config.cfg_access.window) {
+ u32 read_mask;
+
+ /* Must be bar 0 */
+ if (!valid_bar_access(d, &d->config.cfg_access))
+ errx(1, "Invalid cfg_access to bar%u, offset %u len %u",
+ d->config.cfg_access.cap.bar,
+ d->config.cfg_access.cap.offset,
+ d->config.cfg_access.cap.length);
+
+ /*
+ * Read into the window. The mask we use is set by
+ * len, *not* this read!
+ */
+ read_mask = (1ULL<<(8*d->config.cfg_access.cap.length))-1;
+ d->config.cfg_access.window
+ = emulate_mmio_read(d,
+ d->config.cfg_access.cap.offset,
+ read_mask);
+ verbose("Window read %#x/%#x from bar %u, offset %u len %u\n",
+ d->config.cfg_access.window, read_mask,
+ d->config.cfg_access.cap.bar,
+ d->config.cfg_access.cap.offset,
+ d->config.cfg_access.cap.length);
+ }
ioread(port - PCI_CONFIG_DATA, d->config_words[reg], mask, val);
}