On 14/12/2015 15:39, Alexis D...t wrote:
> It fixes the slow-down of VM running with pci-passthrough, since some MTRR
> range changed from MTRR_TYPE_WRBACK to MTRR_TYPE_UNCACHABLE.
>
> Fixes: fa61213746a ("KVM: MTRR: simplify kvm_mtrr_get_guest_memory_type")
> Bugzilla: (https://bugzilla.kernel.org/show_bug.cgi?id=107561)
>
> Signed-off-by: Alexis Dambricourt <alexis.dambricourt@xxxxxxxxx>
> ---
> arch/x86/kvm/mtrr.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
> index 9e8bf13..adc54e1 100644
> --- a/arch/x86/kvm/mtrr.c
> +++ b/arch/x86/kvm/mtrr.c
> @@ -267,7 +267,7 @@ static int fixed_mtrr_addr_to_seg(u64 addr)
>
> for (seg = 0; seg < seg_num; seg++) {
> mtrr_seg = &fixed_seg_table[seg];
> - if (mtrr_seg->start >= addr && addr < mtrr_seg->end)
> + if (mtrr_seg->start <= addr && addr < mtrr_seg->end)
So this if could never be true.
> return seg;
> }
>
> --
>
While that's embarrassing, :) it would only apply to memory in the 640K-1M
range, while the logs in the BZ have
nov 22 17:06:49 Core-i7-5.lan kernel: vmx_get_mt_mask got the following: cpu=6, vcpu=0, gfn=67fe00, MMIO=0, cache=0
Note that this is a page above 4GB, which is why in the BZ I thought that
the culprit was MAXPHYADDR (and I still believe it is, at least for the
OVMF case---there are probably two bugs, and your patch fixes one).
Paolo
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