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Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V
From: |
Roman Kagan |
Subject: |
Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure |
Date: |
Wed, 21 Mar 2018 15:10:01 +0300 |
User-agent: |
Mutt/1.9.2 (2017-12-15) |
On Tue, Mar 20, 2018 at 06:35:00PM +0100, Vitaly Kuznetsov wrote:
> Requiring tsc_is_stable_and_known() is too restrictive: even without INVTCS
> nested Hyper-V-on-KVM enables TSC pages for its guests e.g. when
> Reenlightenment MSRs are present. Presence of frequency MSRs doesn't mean
> these frequencies are stable, it just means they're available for reading.
>
> Signed-off-by: Vitaly Kuznetsov <address@hidden>
> ---
> target/i386/kvm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 7d9f9ca0b1..74fc3d3b2c 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -651,7 +651,7 @@ static int hyperv_handle_properties(CPUState *cs)
> env->features[FEAT_HYPERV_EAX] |= HV_TIME_REF_COUNT_AVAILABLE;
> env->features[FEAT_HYPERV_EAX] |= HV_REFERENCE_TSC_AVAILABLE;
>
> - if (has_msr_hv_frequencies && tsc_is_stable_and_known(env)) {
> + if (has_msr_hv_frequencies && env->tsc_khz) {
> env->features[FEAT_HYPERV_EAX] |= HV_ACCESS_FREQUENCY_MSRS;
> env->features[FEAT_HYPERV_EDX] |= HV_FREQUENCY_MSRS_AVAILABLE;
> }
I suggest that we add a corresponding cpu property here, too. The guest
may legitimately rely on these msrs when it sees the support in CPUID,
and migrating from a kernel with the feature supported (4.14+) to an
older one will make it crash.
Roman.
- [Qemu-devel] [PATCH v3 0/2] i386/kvm: TSC page clocksource for Hyper-V-on-KVM fixes, Vitaly Kuznetsov, 2018/03/20
- [Qemu-devel] [PATCH v3 1/2] i386/kvm: add support for Hyper-V reenlightenment MSRs, Vitaly Kuznetsov, 2018/03/20
- [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Vitaly Kuznetsov, 2018/03/20
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure,
Roman Kagan <=
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Vitaly Kuznetsov, 2018/03/21
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Roman Kagan, 2018/03/21
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Eduardo Habkost, 2018/03/21
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Roman Kagan, 2018/03/22
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Eduardo Habkost, 2018/03/22
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Roman Kagan, 2018/03/22
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Eduardo Habkost, 2018/03/22
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Roman Kagan, 2018/03/23
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Eduardo Habkost, 2018/03/23
- Re: [Qemu-devel] [PATCH v3 2/2] i386/kvm: lower requirements for Hyper-V frequency MSRs exposure, Roman Kagan, 2018/03/26