linux-kernel - Re: [PATCH] KVM: x86: Synchronize APIC State with QEMU when irqchip=split

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Message-ID: <f009b0c5dea8e50a7fa03056b177bcedcfd21132.camel@infradead.org>
Date: Wed, 13 Aug 2025 12:03:18 +0200
From: David Woodhouse <dwmw2@...radead.org>
To: hugo lee <cs.hugolee@...il.com>
Cc: Sean Christopherson <seanjc@...gle.com>, pbonzini@...hat.com, 
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com,  hpa@...or.com, x86@...nel.org,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org,  Yuguo Li
 <hugoolli@...cent.com>
Subject: Re: [PATCH] KVM: x86: Synchronize APIC State with QEMU when
 irqchip=split

On Wed, 2025-08-13 at 17:30 +0800, hugo lee wrote:
> 
> Sorry for the misleading, what I was going to say is
> do only cpu_synchroniza_state() in this new userspace exit reason
> and do nothing on the PIT.
> So QEMU will ignore the PIT as the guests do.
> 
> The resample is great and needed, but the synchronization
> makes more sense to me on this question.

So if the guest doesn't actually quiesce the PIT, QEMU will *still*
keep waking up to waggle the PIT output pin, it's just that QEMU won't
bother telling the kernel about it?

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