KVM x86/xen: add an override for PVCLOCK_TSC_STABLE_BIT

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Unless explicitly told to do so (by passing 'clocksource=tsc' and
'tsc=stable:socket', and then jumping through some hoops concerning
potential CPU hotplug) Xen will never use TSC as its clocksource.
Hence, by default, a Xen guest will not see PVCLOCK_TSC_STABLE_BIT set
in either the primary or secondary pvclock memory areas. This has
led to bugs in some guest kernels which only become evident if
PVCLOCK_TSC_STABLE_BIT *is* set in the pvclocks. Hence, to support
such guests, give the VMM a new Xen HVM config flag to tell KVM to
forcibly clear the bit in the Xen pvclocks.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20231102162128.2353459-1-paul@xen.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

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Paul Durrant 2023-11-02 16:21:28 +00:00 • committed by Sean Christopherson

parent e9e60c82fe

commit 6d72283526

4 changed files with 38 additions and 6 deletions

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6

Documentation/virt/kvm/api.rst

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28

arch/x86/kvm/x86.c

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9

arch/x86/kvm/xen.c

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1

include/uapi/linux/kvm.h

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