From: Sean Christopherson <seanjc@google.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com,
Jim Mattson <jmattson@google.com>,
Simon Veith <sveith@amazon.de>,
Jack Allister <jalliste@amazon.co.uk>, paul <paul@xen.org>,
Joao Martins <joao.m.martins@oracle.com>
Subject: Re: [PATCH] KVM: x86/xen: Do not corrupt KVM clock in kvm_xen_shared_info_init()
Date: Tue, 9 Apr 2024 17:33:18 -0700 [thread overview]
Message-ID: <ZhXeTvNOByDRTlb4@google.com> (raw)
In-Reply-To: <7e0040f70c629d365e80d13b339a95e0affa6d61.camel@infradead.org>
On Sun, Apr 07, 2024, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
>
> The KVM clock is an interesting thing. It is defined as "nanoseconds
> since the guest was created", but in practice it runs at two *different*
> rates — or three different rates, if you count implementation bugs.
LOL, nice.
> Definition C should simply be eliminated. Commit 451a707813ae ("KVM:
> x86/xen: improve accuracy of Xen timers") worked around it for the
> specific case of Xen timers, which are defined in terms of the KVM clock
> and suffered from a continually increasing error in timer expiry times.
IIUC, there should probably be a "But that's a problem for a different day" line
after this. I.e. describing 'C' is purely for context, and removing the
KVM_REQ_MASTERCLOCK_UPDATE request doesn't move the needle on eliminating this
flaw, correct?
next prev parent reply other threads:[~2024-04-10 0:33 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-07 13:15 [PATCH] KVM: x86/xen: Do not corrupt KVM clock in kvm_xen_shared_info_init() David Woodhouse
2024-04-08 11:12 ` Paul Durrant
2024-04-10 0:33 ` Sean Christopherson [this message]
2024-04-10 9:17 ` David Woodhouse
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