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SubjectRe: [PATCH v5 3/3] vfio/pci: Decouple PCI_COMMAND_MEMORY bit checks from is_virtfn
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On 9/10/20 10:59 AM, Matthew Rosato wrote:
> While it is true that devices with is_virtfn=1 will have a Memory Space
> Enable bit that is hard-wired to 0, this is not the only case where we
> see this behavior -- For example some bare-metal hypervisors lack
> Memory Space Enable bit emulation for devices not setting is_virtfn
> (s390). Fix this by instead checking for the newly-added
> no_command_memory bit which directly denotes the need for
> PCI_COMMAND_MEMORY emulation in vfio.
>
> Fixes: abafbc551fdd ("vfio-pci: Invalidate mmaps and block MMIO access on disabled memory")
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>

Polite ping on this patch as the other 2 have now received maintainer
ACKs or reviews. I'm concerned about this popping up in distros as
abafbc551fdd was a CVE fix. Related, see question from the cover:

- Restored the fixes tag to patch 3 (but the other 2 patches are
now pre-reqs -- cc stable 5.8?)

Thanks,
Matt

> ---
> drivers/vfio/pci/vfio_pci_config.c | 24 ++++++++++++++----------
> 1 file changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index d98843f..5076d01 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -406,7 +406,7 @@ bool __vfio_pci_memory_enabled(struct vfio_pci_device *vdev)
> * PF SR-IOV capability, there's therefore no need to trigger
> * faults based on the virtual value.
> */
> - return pdev->is_virtfn || (cmd & PCI_COMMAND_MEMORY);
> + return pdev->no_command_memory || (cmd & PCI_COMMAND_MEMORY);
> }
>
> /*
> @@ -520,8 +520,8 @@ static int vfio_basic_config_read(struct vfio_pci_device *vdev, int pos,
>
> count = vfio_default_config_read(vdev, pos, count, perm, offset, val);
>
> - /* Mask in virtual memory enable for SR-IOV devices */
> - if (offset == PCI_COMMAND && vdev->pdev->is_virtfn) {
> + /* Mask in virtual memory enable */
> + if (offset == PCI_COMMAND && vdev->pdev->no_command_memory) {
> u16 cmd = le16_to_cpu(*(__le16 *)&vdev->vconfig[PCI_COMMAND]);
> u32 tmp_val = le32_to_cpu(*val);
>
> @@ -589,9 +589,11 @@ static int vfio_basic_config_write(struct vfio_pci_device *vdev, int pos,
> * shows it disabled (phys_mem/io, then the device has
> * undergone some kind of backdoor reset and needs to be
> * restored before we allow it to enable the bars.
> - * SR-IOV devices will trigger this, but we catch them later
> + * SR-IOV devices will trigger this - for mem enable let's
> + * catch this now and for io enable it will be caught later
> */
> - if ((new_mem && virt_mem && !phys_mem) ||
> + if ((new_mem && virt_mem && !phys_mem &&
> + !pdev->no_command_memory) ||
> (new_io && virt_io && !phys_io) ||
> vfio_need_bar_restore(vdev))
> vfio_bar_restore(vdev);
> @@ -1734,12 +1736,14 @@ int vfio_config_init(struct vfio_pci_device *vdev)
> vconfig[PCI_INTERRUPT_PIN]);
>
> vconfig[PCI_INTERRUPT_PIN] = 0; /* Gratuitous for good VFs */
> -
> + }
> + if (pdev->no_command_memory) {
> /*
> - * VFs do no implement the memory enable bit of the COMMAND
> - * register therefore we'll not have it set in our initial
> - * copy of config space after pci_enable_device(). For
> - * consistency with PFs, set the virtual enable bit here.
> + * VFs and devices that set pdev->no_command_memory do not
> + * implement the memory enable bit of the COMMAND register
> + * therefore we'll not have it set in our initial copy of
> + * config space after pci_enable_device(). For consistency
> + * with PFs, set the virtual enable bit here.
> */
> *(__le16 *)&vconfig[PCI_COMMAND] |=
> cpu_to_le16(PCI_COMMAND_MEMORY);
>

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