>From what I see in my case, it was especially gfn from 0x0 to 0xA0
which are deadly impacted by the wrong cache property.
2015-12-14 16:36 GMT+01:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
>
>
> 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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