On Wed, Apr 01, 2015 at 06:12:18PM +0800, Jason Wang wrote:
> >> diff --git a/hw/pci/msix.c b/hw/pci/msix.c
> >> index 24de260..8c6d8f3 100644
> >> --- a/hw/pci/msix.c
> >> +++ b/hw/pci/msix.c
> >> @@ -291,33 +291,44 @@ int msix_init(struct PCIDevice *dev, unsigned
> >>short nentries,
> >> }
> >> int msix_init_exclusive_bar(PCIDevice *dev, unsigned short
> >>nentries,
> >> - uint8_t bar_nr)
> >> + uint8_t bar_nr, bool legacy_layout)
> >> {
> >> int ret;
> >> char *name;
> >> -
> >> - /*
> >> - * Migration compatibility dictates that this remains a 4k
> >> - * BAR with the vector table in the lower half and PBA in
> >> - * the upper half. Do not use these elsewhere!
> >> - */
> >> -#define MSIX_EXCLUSIVE_BAR_SIZE 4096
> >> -#define MSIX_EXCLUSIVE_BAR_TABLE_OFFSET 0
> >> -#define MSIX_EXCLUSIVE_BAR_PBA_OFFSET (MSIX_EXCLUSIVE_BAR_SIZE / 2)
> >> -#define MSIX_EXCLUSIVE_CAP_OFFSET 0
> >> -
> >> - if (nentries * PCI_MSIX_ENTRY_SIZE >
> >>MSIX_EXCLUSIVE_BAR_PBA_OFFSET) {
> >> - return -EINVAL;
> >> + uint32_t bar_size;
> >> + uint32_t bar_pba_offset;
> >> +
> >> + if (legacy_layout) {
> >> + /*
> >> + * Migration compatibility dictates that this remains a 4k
> >> + * BAR with the vector table in the lower half and PBA in
> >> + * the upper half. Do not use these elsewhere!
> >> + */
> >> + bar_size = 4096;
> >> + bar_pba_offset = bar_size / 2;
> >> +
> >> + if (nentries * PCI_MSIX_ENTRY_SIZE > bar_pba_offset) {
> >> + return -EINVAL;
> >> + }
> >
> >So this takes pains to behave in a compatible
> >way when more than 128 vectors are requested.
> >But since we only had up to 64 VQs, why does
> >some a configuration make sense?
>
> This question could also be asked for the code even without this patch. Spec
> does not clarify this and if we think vectors>=128 is not a valid
> configuration with only 64 VQs, qemu should fail and quit instead of a
> warning. Unfortunately we don't do this and leave a chance for user to use
> it.
I agree with this as a general design principle.
And it's typically even better to just support what
the user requested, even if it doesn't make sense.
--
MST
