On Wed, Feb 15, 2017 at 10:49:47PM +0200, Michael S. Tsirkin wrote:
> VFIO actually wants to create a capability with ID == 0.
> This is done to make guest drivers skip the given capability.
> pcie_add_capability then trips up on this capability
> when looking for end of capability list.
>
> To support this use-case, it's easy enough to switch to
> e.g. 0xffffffff for these comparisons - we can be sure
> it will never match a 16-bit capability ID.
>
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
Reviewed-by: Peter Xu <pet...@redhat.com>
Two nits:
(1) maybe we can s/0xffffffff/0xffff/ in the whole patch since ecap_id
is 16 bits
(2) maybe we can add one more sentence in the comment below showing
where the 0xffff thing comes from (it comes from PCIe spec 7.9.2)
Thanks,
> ---
> hw/pci/pcie.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index cbd4bb4..f4dd177 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -610,7 +610,8 @@ bool pcie_cap_is_arifwd_enabled(const PCIDevice *dev)
> * uint16_t ext_cap_size
> */
>
> -static uint16_t pcie_find_capability_list(PCIDevice *dev, uint16_t cap_id,
> +/* Passing a cap_id value > 0xffff will return 0 and put end of list in prev
> */
> +static uint16_t pcie_find_capability_list(PCIDevice *dev, uint32_t cap_id,
> uint16_t *prev_p)
> {
> uint16_t prev = 0;
> @@ -679,9 +680,11 @@ void pcie_add_capability(PCIDevice *dev,
> } else {
> uint16_t prev;
>
> - /* 0 is reserved cap id. use internally to find the last capability
> - in the linked list */
> - next = pcie_find_capability_list(dev, 0, &prev);
> + /*
> + * 0xffffffff is not a valid cap id (it's a 16 bit field). use
> + * internally to find the last capability in the linked list.
> + */
> + next = pcie_find_capability_list(dev, 0xffffffff, &prev);
>
> assert(prev >= PCI_CONFIG_SPACE_SIZE);
> assert(next == 0);
> --
> MST
-- peterx
