linux-kernel - Re: [PATCH][for stable/linux-5.15.y] KVM: VMX: Move preemption timer <=> hrtimer dance to common x86

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Date:   Mon, 3 Apr 2023 15:08:44 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Tudor Ambarus <tudor.ambarus@...aro.org>
Cc:     pbonzini@...hat.com, stable@...r.kernel.org, seanjc@...gle.com,
        joro@...tes.org, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, suravee.suthikulpanit@....com,
        kvm@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, mlevitsk@...hat.com,
        joneslee@...gle.com,
        syzbot+b6a74be92b5063a0f1ff@...kaller.appspotmail.com
Subject: Re: [PATCH][for stable/linux-5.15.y] KVM: VMX: Move preemption timer
 <=> hrtimer dance to common x86

On Wed, Mar 29, 2023 at 03:17:47PM +0000, Tudor Ambarus wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> commit 98c25ead5eda5e9d41abe57839ad3e8caf19500c upstream.
> 
> Handle the switch to/from the hypervisor/software timer when a vCPU is
> blocking in common x86 instead of in VMX.  Even though VMX is the only
> user of a hypervisor timer, the logic and all functions involved are
> generic x86 (unless future CPUs do something completely different and
> implement a hypervisor timer that runs regardless of mode).
> 
> Handling the switch in common x86 will allow for the elimination of the
> pre/post_blocks hooks, and also lets KVM switch back to the hypervisor
> timer if and only if it was in use (without additional params).  Add a
> comment explaining why the switch cannot be deferred to kvm_sched_out()
> or kvm_vcpu_block().
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Message-Id: <20211208015236.1616697-8-seanjc@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> [ta: Fix conflicts in vmx_pre_block and vmx_post_block as per Paolo's
> suggestion. Add Reported-by and Link tags.]
> Reported-by: syzbot+b6a74be92b5063a0f1ff@...kaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?id=489beb3d76ef14cc6cd18125782dc6f86051a605
> Tested-by: Tudor Ambarus <tudor.ambarus@...aro.org>
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
> ---
>  arch/x86/kvm/vmx/vmx.c |  6 ------
>  arch/x86/kvm/x86.c     | 21 +++++++++++++++++++++
>  2 files changed, 21 insertions(+), 6 deletions(-)

Now queued up, thanks.

greg k-h