lkml.org 
[lkml]   [2020]   [Mar]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS
From
Date

> On Mar 7, 2020, at 2:09 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
>
> Andy Lutomirski <luto@kernel.org> writes:
>
>> The ABI is broken and we cannot support it properly. Turn it off.
>>
>> If this causes a meaningful performance regression for someone, KVM
>> can introduce an improved ABI that is supportable.
>>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>> ---
>> arch/x86/kernel/kvm.c | 11 ++++++++---
>> 1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>> index 93ab0cbd304e..71f9f39f93da 100644
>> --- a/arch/x86/kernel/kvm.c
>> +++ b/arch/x86/kernel/kvm.c
>> @@ -318,11 +318,16 @@ static void kvm_guest_cpu_init(void)
>>
>> pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason));
>>
>> -#ifdef CONFIG_PREEMPTION
>> - pa |= KVM_ASYNC_PF_SEND_ALWAYS;
>> -#endif
>> pa |= KVM_ASYNC_PF_ENABLED;
>>
>> + /*
>> + * We do not set KVM_ASYNC_PF_SEND_ALWAYS. With the current
>> + * KVM paravirt ABI, if an async page fault occurs on an early
>> + * memory access in the normal (sync) #PF path or in an NMI
>> + * that happens early in the #PF code, the combination of CR2
>> + * and the APF reason field will be corrupted.
>
> I don't think this can happen. In both cases IF == 0 and that async
> (think host side) page fault will be completely handled on the
> host. There is no injection happening in such a case ever. If it does,
> then yes the host side implementation is buggered, but AFAICT this is
> not the case.

Indeed. But read v2 please.

>
> See also my reply in the other thread:
>
> https://lore.kernel.org/r/87r1y4a3gw.fsf@nanos.tec.linutronix.de
>
> Thanks,
>
> tglx

\
 
 \ /
  Last update: 2020-03-07 15:37    [W:0.094 / U:0.348 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site