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lguest: don't look in console features to find emerg_wr.

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The 1.0 spec clearly states that you must set the ACKNOWLEDGE and
DRIVER status bits before accessing the feature bits.  This is a
problem for the early console code, which doesn't really want to
acknowledge the device (the spec specifically excepts writing to the
console's emerg_wr from the usual ordering constrains).

Instead, we check that the *size* of the device configuration is
sufficient to hold emerg_wr: at worst (if the device doesn't support
the VIRTIO_CONSOLE_F_EMERG_WRITE feature), it will ignore the
writes.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2015-02-13 17:13:43 +10:30
parent d761b03291
commit 55c2d7884e
1 changed files with 24 additions and 33 deletions
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57
arch/x86/lguest/boot.c
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@ -1222,15 +1222,13 @@ static void set_cfg_window(u32 cfg_offset, u32 off)
off);
}
static u32 read_bar_via_cfg(u32 cfg_offset, u32 off)
{
set_cfg_window(cfg_offset, off);
return read_pci_config(0, 1, 0,
cfg_offset + sizeof(struct virtio_pci_cap));
}
static void write_bar_via_cfg(u32 cfg_offset, u32 off, u32 val)
{
/*
* We could set this up once, then leave it; nothing else in the *
* kernel should touch these registers. But if it went wrong, that
* would be a horrible bug to find.
*/
set_cfg_window(cfg_offset, off);
write_pci_config(0, 1, 0,
cfg_offset + sizeof(struct virtio_pci_cap), val);
@ -1239,8 +1237,9 @@ static void write_bar_via_cfg(u32 cfg_offset, u32 off, u32 val)
static void probe_pci_console(void)
{
u8 cap, common_cap = 0, device_cap = 0;
/* Offsets within BAR0 */
u32 common_offset, device_offset;
/* Offset within BAR0 */
u32 device_offset;
u32 device_len;
/* Avoid recursive printk into here. */
console_cfg_offset = -1;
@ -1263,7 +1262,7 @@ static void probe_pci_console(void)
u8 vndr = read_pci_config_byte(0, 1, 0, cap);
if (vndr == PCI_CAP_ID_VNDR) {
u8 type, bar;
u32 offset;
u32 offset, length;
type = read_pci_config_byte(0, 1, 0,
cap + offsetof(struct virtio_pci_cap, cfg_type));
@ -1271,18 +1270,15 @@ static void probe_pci_console(void)
cap + offsetof(struct virtio_pci_cap, bar));
offset = read_pci_config(0, 1, 0,
cap + offsetof(struct virtio_pci_cap, offset));
length = read_pci_config(0, 1, 0,
cap + offsetof(struct virtio_pci_cap, length));
switch (type) {
case VIRTIO_PCI_CAP_COMMON_CFG:
if (bar == 0) {
common_cap = cap;
common_offset = offset;
}
break;
case VIRTIO_PCI_CAP_DEVICE_CFG:
if (bar == 0) {
device_cap = cap;
device_offset = offset;
device_len = length;
}
break;
case VIRTIO_PCI_CAP_PCI_CFG:
@ -1292,32 +1288,27 @@ static void probe_pci_console(void)
}
cap = read_pci_config_byte(0, 1, 0, cap + PCI_CAP_LIST_NEXT);
}
if (!common_cap || !device_cap || !console_access_cap) {
if (!device_cap || !console_access_cap) {
printk(KERN_ERR "lguest: No caps (%u/%u/%u) in console!\n",
common_cap, device_cap, console_access_cap);
return;
}
#define write_common_config(reg, val) \
write_bar_via_cfg(console_access_cap, \
common_offset+offsetof(struct virtio_pci_common_cfg,reg),\
val)
#define read_common_config(reg) \
read_bar_via_cfg(console_access_cap, \
common_offset+offsetof(struct virtio_pci_common_cfg,reg))
/* Check features: they must offer EMERG_WRITE */
write_common_config(device_feature_select, 0);
if (!(read_common_config(device_feature)
& (1 << VIRTIO_CONSOLE_F_EMERG_WRITE))) {
printk(KERN_ERR "lguest: console missing EMERG_WRITE\n");
/*
* Note that we can't check features, until we've set the DRIVER
* status bit. We don't want to do that until we have a real driver,
* so we just check that the device-specific config has room for
* emerg_wr. If it doesn't support VIRTIO_CONSOLE_F_EMERG_WRITE
* it should ignore the access.
*/
if (device_len < (offsetof(struct virtio_console_config, emerg_wr)
+ sizeof(u32))) {
printk(KERN_ERR "lguest: console missing emerg_wr field\n");
return;
}
console_cfg_offset = device_offset;
printk(KERN_INFO "lguest: Console via virtio-pci emerg_wr\n");
}
/*