linux-kernel - Re: [PATCH v2 3/5] KVM: SVM: Manually context switch DEBUGCTL if LBR virtualization is disabled

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Message-ID: <Z8B3IvwtGqz8aCHD@google.com>
Date: Thu, 27 Feb 2025 06:30:58 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Ravi Bangoria <ravi.bangoria@....com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Xiaoyao Li <xiaoyao.li@...el.com>, rangemachine@...il.com, whanos@...gal.fun
Subject: Re: [PATCH v2 3/5] KVM: SVM: Manually context switch DEBUGCTL if LBR
 virtualization is disabled

On Thu, Feb 27, 2025, Ravi Bangoria wrote:
> > Somewhat related but independent: CPU automatically clears DEBUGCTL[BTF]
> > on #DB exception. So, when DEBUGCTL is save/restored by KVM (i.e. when
> > LBR virtualization is disabled), it's KVM's responsibility to clear
> > DEBUGCTL[BTF].
> 
> Found this with below KUT test.
> 
> (I wasn't sure whether I should send a separate series for kernel fix + KUT
> patch, or you can squash kernel fix in your patch and I shall send only KUT
> patch. So for now, sending it as a reply here.)

Go ahead and send the KUT test.  They two repositories evolve independently no
matter the order, just put a Link to lore of the kernel fix/discussion.

Thanks a ton for writing a test!