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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d3e44057beb8db40d90e838265df7f4a2752361a.camel@infradead.org>
Date: Tue, 12 Aug 2025 12:46:01 +0200
From: David Woodhouse <dwmw2@...radead.org>
To: hugo lee <cs.hugolee@...il.com>, Sean Christopherson <seanjc@...gle.com>
Cc: 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 Tue, 2025-08-12 at 18:08 +0800, hugo lee wrote:
> 
> On some legacy bios images using guests, they may disable PIT
> after booting.

Do you mean they may *not* disable the PIT after booting? Linux had
that problem for a long time, until I fixed it with
https://git.kernel.org/torvalds/c/70e6b7d9ae3

> When irqchip=split is on, qemu will keep kicking the guest and try to
> get the Big QEMU Lock.

If it's the PIT, surely QEMU will keep stealing time pointlessly unless
we actually disable the PIT itself? Not just the IRQ delivery? Or do
you use this to realise that the IRQ output from the PIT isn't going
anywhere and thus disable the event in QEMU completely? 

Download attachment "smime.p7s" of type "application/pkcs7-signature" (5069 bytes)