linux-kernel - Re: [RFC PATCH v2 10/23] KVM: TDX: Enable huge page splitting under write kvm->mmu

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Message-ID: <aTooGaNq353hlGkE@yzhao56-desk.sh.intel.com>
Date: Thu, 11 Dec 2025 10:10:33 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "sagis@...gle.com" <sagis@...gle.com>, "Du, Fan" <fan.du@...el.com>, "Li,
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Subject: Re: [RFC PATCH v2 10/23] KVM: TDX: Enable huge page splitting under
 write kvm->mmu_lock

On Thu, Dec 11, 2025 at 03:49:26AM +0800, Edgecombe, Rick P wrote:
> On Wed, 2025-12-10 at 11:16 -0600, Sagi Shahar wrote:
> > From what I saw this is not just a
> > theoretical race but happens every time I try to boot a VM
I don't think we mentioned that the retry for TDX_INTERRUPTED_RESTARTABLE is
theoretical, did we? :)

On my SPR, to boot a VM with 8 vCPUs 8 GB memory, on average there are
271.4 demotes, with 1.1 retry for TDX_INTERRUPTED_RESTARTABLE.

   #    | demote cnt | retry cnt (for TDX_INTERRUPTED_RESTARTABLE)
--------|------------|----------
   1    |    271     |    2
   2    |    273     |    0
   3    |    271     |    1
   4    |    270     |    2
   5    |    271     |    3
   6    |    271     |    0
   7    |    274     |    0
   8    |    270     |    0
   9    |    271     |    2
  10    |    272     |    0
 
> Oh, interesting.
> 
> > , even for a
> > small VM with 4 VCPUs and 8GB of memory.
> 
> It probably more matters what else is happening on the system to cause a host
> interrupt.
Agreed.