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

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Message-ID: <ZyDm25/oSBfuUpqj@tpad>
Date: Tue, 29 Oct 2024 10:44:59 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: "Nikunj A. Dadhania" <nikunj@....com>
Cc: Xiaoyao Li <xiaoyao.li@...el.com>,
	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

On Tue, Oct 29, 2024 at 09:34:58AM +0530, Nikunj A. Dadhania wrote:
> 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/

Please don't, haven't tested specifically the patches above.

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