Thank you for offering your valuable advice.
Will send the updated version soon.
> -----Original Message-----
> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Saturday, March 20, 2021 3:27 AM
> To: Gao, Fred <fred.gao@xxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; Zhenyu Wang
> <zhenyuw@xxxxxxxxxxxxxxx>; Fonn, Swee Yee <swee.yee.fonn@xxxxxxxxx>
> Subject: Re: [PATCH v4] vfio/pci: Add support for opregion v2.1+
>
> 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);
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/intel-gfx
