Messages in this thread | | | From | Paul Durrant <> | Date | Fri, 19 Apr 2024 16:49:49 +0100 | Subject | Re: [PATCH 06/10] KVM: x86: Add KVM_VCPU_TSC_SCALE and fix the documentation on TSC migration |
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On 18/04/2024 20:34, David Woodhouse wrote: > From: David Woodhouse <dwmw@amazon.co.uk> > > The documentation on TSC migration using KVM_VCPU_TSC_OFFSET is woefully > inadequate. It ignores TSC scaling, and ignores the fact that the host > TSC may differ from one host to the next (and in fact because of the way > the kernel calibrates it, it generally differs from one boot to the next > even on the same hardware). > > Add KVM_VCPU_TSC_SCALE to extract the actual scale ratio and frac_bits, > and attempt to document the *awful* process that we're requiring userspace > to follow to merely preserve the TSC across migration. > > I may have thrown up in my mouth a little when writing that documentation. > It's an awful API. If we do this, we should be ashamed of ourselves. > (I also haven't tested the documented process yet). > > Let's use Simon's KVM_VCPU_TSC_VALUE instead. > https://lore.kernel.org/all/20230202165950.483430-1-sveith@amazon.de/ > > Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> > --- > Documentation/virt/kvm/devices/vcpu.rst | 115 ++++++++++++++++++------ > arch/x86/include/uapi/asm/kvm.h | 6 ++ > arch/x86/kvm/x86.c | 15 ++++ > 3 files changed, 109 insertions(+), 27 deletions(-) >
Reviewed-by: Paul Durrant <paul@xen.org>
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