On Tue, 2 Mar 2021 21:02:20 +0800
Fred Gao <fred.gao@xxxxxxxxx> wrote:
> Before opregion version 2.0 VBT data is stored in opregion mailbox #4,
> However, When VBT data exceeds 6KB size and cannot be within mailbox #4
> starting from opregion v2.0+, Extended VBT region, next to opregion, is
> used to hold the VBT data, so the total size will be opregion size plus
> extended VBT region size.
>
> since opregion v2.0 with physical host VBT address should not be
> practically available for end user, it is not supported.
>
> Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
> Signed-off-by: Swee Yee Fonn <swee.yee.fonn@xxxxxxxxx>
> Signed-off-by: Fred Gao <fred.gao@xxxxxxxxx>
> ---
> drivers/vfio/pci/vfio_pci_igd.c | 49 +++++++++++++++++++++++++++++++++
> 1 file changed, 49 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci_igd.c b/drivers/vfio/pci/vfio_pci_igd.c
> index 53d97f459252..4edb8afcdbfc 100644
> --- a/drivers/vfio/pci/vfio_pci_igd.c
> +++ b/drivers/vfio/pci/vfio_pci_igd.c
> @@ -21,6 +21,10 @@
> #define OPREGION_SIZE (8 * 1024)
> #define OPREGION_PCI_ADDR 0xfc
>
> +#define OPREGION_RVDA 0x3ba
> +#define OPREGION_RVDS 0x3c2
> +#define OPREGION_VERSION 0x16
> +
> static size_t vfio_pci_igd_rw(struct vfio_pci_device *vdev, char __user *buf,
> size_t count, loff_t *ppos, bool iswrite)
> {
> @@ -58,6 +62,7 @@ static int vfio_pci_igd_opregion_init(struct vfio_pci_device *vdev)
> u32 addr, size;
> void *base;
> int ret;
> + u16 version;
>
> ret = pci_read_config_dword(vdev->pdev, OPREGION_PCI_ADDR, &addr);
> if (ret)
> @@ -83,6 +88,50 @@ static int vfio_pci_igd_opregion_init(struct vfio_pci_device *vdev)
>
> size *= 1024; /* In KB */
>
> + /*
> + * Support opregion v2.1+
> + * When VBT data exceeds 6KB size and cannot be within mailbox #4
s/#4/#4, then the/
> + * Extended VBT region, next to opregion, is used to hold the VBT data.
> + * RVDA (Relative Address of VBT Data from Opregion Base) and RVDS
> + * (VBT Data Size) from opregion structure member are used to hold the
> + * address from region base and size of VBT data while RVDA/RVDS
> + * are not defined before opregion 2.0.
> + *
> + * opregion 2.0: rvda is the physical VBT address.
Let's expand the comment to include why this is a problem to support
(virtualization of this register would be required in userspace) and why
we're choosing not to manipulate this into a 2.1+ table, which I think
is both the practical lack of v2.0 tables in use and any implicit
dependencies software may have on the OpRegion version.
> + *
> + * opregion 2.1+: rvda is unsigned, relative offset from
> + * opregion base, and should never point within opregion.
And for our purposes must exactly follow the base opregion to avoid
exposing unknown host memory to userspace, ie. provide a more
descriptive justification for the 2nd error condition below.
> + */
> + version = le16_to_cpu(*(__le16 *)(base + OPREGION_VERSION));
> + if (version >= 0x0200) {
> + u64 rvda;
> + u32 rvds;
> +
> + rvda = le64_to_cpu(*(__le64 *)(base + OPREGION_RVDA));
> + rvds = le32_to_cpu(*(__le32 *)(base + OPREGION_RVDS));
> + if (rvda && rvds) {
> + /* no support for opregion v2.0 with physical VBT address */
> + if (version == 0x0200) {
> + memunmap(base);
> + pci_err(vdev->pdev,
> + "IGD passthrough does not support opregion\n"
> + "version 0x%x with physical rvda 0x%llx\n", version, rvda);
Why do we need a new line midway through this log message?
s/passthrough/assignment/
In testing the version you include the leading zero, do you also want
that leading zero in the printed version, ie. %04x?
If we get to this code, we already know that both rvda and rvds are
non-zero, why is it useful to print the rvda value in this error
message? For example, we could print:
"IGD assignment does not support opregion version 0x%04x with an extended VBT region"
> + return -EINVAL;
> + }
> +
> + if ((u32)rvda != size) {
What allows us to assume rvda is a 32bit value given that it's a 64bit
register? It seems safer not to include this cast.
> + memunmap(base);
> + pci_err(vdev->pdev,
> + "Extended VBT does not follow opregion !\n"
> + "opregion version 0x%x:rvda 0x%llx\n", version, rvda);
Again I'm not sure about the usefulness of printing the rvda value on
its own. Without knowing the size value it seems meaningless. Like
above, get rid of the mid-error new line and random space if you keep
the exclamation point.
> + return -EINVAL;
> + }
> +
> + /* region size for opregion v2.0+: opregion and VBT size */
> + size += rvds;
RVDS is defined as size in bytes, not in kilobytes like the base
opregion size, right? Let's include that clarification in the comment
since the spec is private. Thanks,
Alex
> + }
> + }
> +
> if (size != OPREGION_SIZE) {
> memunmap(base);
> base = memremap(addr, size, MEMREMAP_WB);
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