Commit 55c2d788 authored by Rusty Russell's avatar Rusty Russell
Browse files

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



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: default avatarRusty Russell <rusty@rustcorp.com.au>
parent d761b032

arch/x86/lguest/boot.c

+24 −33
Original line number Diff line number Diff line
@@ -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");

}



/*

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