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Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip
From: |
Vitaly Kuznetsov |
Subject: |
Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off |
Date: |
Tue, 22 Sep 2020 17:38:12 +0200 |
Eduardo Habkost <ehabkost@redhat.com> writes:
> This addresses the following crash when running Linux v5.8
> with kernel-irqchip=off:
>
> qemu-system-x86_64: error: failed to set MSR 0x4b564d02 to 0x0
> qemu-system-x86_64: ../target/i386/kvm.c:2714: kvm_buf_set_msrs: Assertion
> `ret == cpu->kvm_msr_buf->nmsrs' failed.
>
> There is a kernel-side fix for the issue too (kernel commit
> d831de177217 "KVM: x86: always allow writing '0' to
> MSR_KVM_ASYNC_PF_EN"), but it's nice to simply not trigger
> the bug if running an older kernel.
>
> Fixes: https://bugs.launchpad.net/bugs/1896263
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
> target/i386/kvm.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 9efb07e7c83..1492f41349f 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -2818,7 +2818,12 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
> kvm_msr_entry_add(cpu, MSR_IA32_TSC, env->tsc);
> kvm_msr_entry_add(cpu, MSR_KVM_SYSTEM_TIME, env->system_time_msr);
> kvm_msr_entry_add(cpu, MSR_KVM_WALL_CLOCK, env->wall_clock_msr);
> - if (env->features[FEAT_KVM] & (1 << KVM_FEATURE_ASYNC_PF)) {
> + /*
> + * Some kernel versions (v5.8) won't let MSR_KVM_ASYNC_PF_EN to be
> set
> + * at all if kernel-irqchip=off, so don't try to set it in that case.
> + */
> + if (env->features[FEAT_KVM] & (1 << KVM_FEATURE_ASYNC_PF) &&
> + kvm_irqchip_in_kernel()) {
> kvm_msr_entry_add(cpu, MSR_KVM_ASYNC_PF_EN,
> env->async_pf_en_msr);
> }
> if (env->features[FEAT_KVM] & (1 << KVM_FEATURE_PV_EOI)) {
I'm not sure kvm_irqchip_in_kernel() was required before we switched to
interrupt-based APF (as we were always injecting #PF) but with
kernel-5.8+ this should work. We'll need to merge this with
https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg02963.html
(queued by Paolo) and
https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg06196.html
which fixes a bug in it.
as kvm_irqchip_in_kernel() should go around both KVM_FEATURE_ASYNC_PF
and KVM_FEATURE_ASYNC_PF_INT I believe.
--
Vitaly
- [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off, Eduardo Habkost, 2020/09/22
- Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off,
Vitaly Kuznetsov <=
- Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off, Eduardo Habkost, 2020/09/22
- Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off, Vitaly Kuznetsov, 2020/09/22
- Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off, Eduardo Habkost, 2020/09/22
- Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off, Paolo Bonzini, 2020/09/22
- Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off, Eduardo Habkost, 2020/09/22
- Re: [PATCH] i386: Don't try to set MSR_KVM_ASYNC_PF_EN if kernel-irqchip=off, Paolo Bonzini, 2020/09/22