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

[Greg KH]

On Wed, Mar 29, 2023 at 03:17:47PM +0000, Tudor Ambarus wrote:
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Message-Id: <20211208015236.1616697-8-seanjc@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> [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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://syzkaller.appspot.com/bug?id=489beb3d76ef14cc6cd18125782dc6f86051a605
> Tested-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx>
> Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx>
> ---
>  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