linux-kernel - Re: [PATCH 0/2] KVM: kvm-coco-queue: Support protected TSC

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Message-ID: <714ab7a2-69fa-b08d-deae-6eb91ecba95b@amd.com>
Date: Tue, 29 Oct 2024 09:34:58 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Marcelo Tosatti <mtosatti@...hat.com>, Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Isaku Yamahata <isaku.yamahata@...el.com>, kvm@...r.kernel.org,
 pbonzini@...hat.com, Sean Christopherson <seanjc@...gle.com>,
 chao.gao@...el.com, rick.p.edgecombe@...el.com, yan.y.zhao@...el.com,
 linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
 Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 0/2] KVM: kvm-coco-queue: Support protected TSC

Hello Marcelo

On 10/28/2024 10:12 PM, Marcelo Tosatti wrote:
> On Sun, Oct 27, 2024 at 10:06:17PM +0800, Xiaoyao Li wrote:
>> On 10/26/2024 12:24 AM, Marcelo Tosatti wrote:
>>> On Mon, Oct 14, 2024 at 08:17:19PM +0530, Nikunj A. Dadhania wrote:
>>>> Hi Isaku,
>>>>
>>>> On 10/12/2024 1:25 PM, Isaku Yamahata wrote:
>>>>> Choose the first one.  With this patch series, SEV-SNP secure TSC can be
>>>>> supported.
>>>>
>>>> I am not sure how will this help SNP Secure TSC, as the GUEST_TSC_OFFSET and
>>>> GUEST_TSC_SCALE are only available to the guest.
>>>
>>> Nikunj,
>>>
>>> FYI:
>>>
>>> SEV-SNP processors (at least the one below) do not seem affected by this problem.
>>
>> Did you apply Secure TSC patches of (guest kernel, KVM and QEMU) manualy?
>> because none of them are merged. 
> 
> Yes. cyclictest latency, on a system configured with tuned
> realtime-virtual-host/realtime-virtual-guest tuned profiles,
> goes from 30us to 50us.

Would you be ok if I include your Tested-by in the next version of my Secure TSC patches?

https://lore.kernel.org/lkml/20241028053431.3439593-1-nikunj@amd.com/

>> Otherwise, I think SNP guest is still using
>> KVM emulated TSC.
> 
> Not in the case the test was made.
> 

Regards,
Nikunj