From: Paolo Bonzini <pbonzini@redhat.com>
To: "Daniel P. Berrangé" <berrange@redhat.com>
Cc: qemu-devel@nongnu.org, Vadim Rozenfeld <vrozenfe@redhat.com>
Subject: Re: [PATCH] target/i386: introduce CPU property to work around Windows reset bug
Date: Thu, 24 Mar 2022 18:13:03 +0100 [thread overview]
Message-ID: <78c4b687-473f-e3db-fcfd-9525e9a5c8f9@redhat.com> (raw)
In-Reply-To: <6bad2204-4a21-19e7-e2f6-3ef30632bda4@redhat.com>
On 3/24/22 12:24, Paolo Bonzini wrote:
> That said, the VMware kbase does paint a slightly different picture. It
> implies that starting with hardware version 11 rebooting Windows is done
> through a hard reset instead of INIT. I'm not sure how that would be
> done, but in the meanwhile our fix should take care of do_cpu_init as well.
Ok, so here are my findings:
- Windows resets the system by writing 0xFE to port 0x64. This is a
hard reset on QEMU, but presumably it was a soft reset (INIT) on VMware
until version 10.
- QEMU _does_ try to write 0 to the TSC on hard reset. But KVM special
cases 0 as "somebody is trying to hot-plug a new CPU" and wants to help
out, so it keeps the CPU synchronized with the previous TSC.
So this is a pretty clear-cut QEMU bug. It can be fixed by e.g. writing
1 to the TSC instead of 0.
Paolo
next prev parent reply other threads:[~2022-03-24 17:17 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-24 8:23 [PATCH] target/i386: introduce CPU property to work around Windows reset bug Paolo Bonzini
2022-03-24 9:13 ` Daniel P. Berrangé
2022-03-24 9:15 ` Daniel P. Berrangé
2022-03-24 9:42 ` Paolo Bonzini
2022-03-24 11:03 ` Daniel P. Berrangé
2022-03-24 11:24 ` Paolo Bonzini
2022-03-24 17:13 ` Paolo Bonzini [this message]
2022-03-24 17:37 ` Daniel P. Berrangé
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