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Peter Anvin" , Paolo Bonzini , Ingo Molnar Subject: Re: [PATCH 2/3] KVM: x86: guest debug: don't inject interrupts while single stepping Message-ID: References: <1259724f-1bdb-6229-2772-3192f6d17a4a@siemens.com> <71ae8b75c30fd0f87e760216ad310ddf72d31c7b.camel@redhat.com> <2a44c302-744e-2794-59f6-c921b895726d@siemens.com> <1d27b215a488f8b8fc175e97c5ab973cc811922d.camel@redhat.com> <727e5ef1-f771-1301-88d6-d76f05540b01@siemens.com> <31c0bba9-0399-1f15-a59b-a8f035e366e8@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <31c0bba9-0399-1f15-a59b-a8f035e366e8@siemens.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 16, 2021, Jan Kiszka wrote: > On 16.03.21 17:50, Sean Christopherson wrote: > > Rather than block all events in KVM, what about having QEMU "pause" the timer? > > E.g. save MSR_TSC_DEADLINE and APIC_TMICT (or inspect the guest to find out > > which flavor it's using), clear them to zero, then restore both when > > single-stepping is disabled. I think that will work? > > > > No one can stop the clock, and timers are only one source of interrupts. > Plus they do not all come from QEMU, some also from KVM or in-kernel > sources directly. But are any other sources of interrupts a chronic problem? I 100% agree that this would not be a robust solution, but neither is blocking events in KVM. At least with this approach, the blast radius is somewhat contained. > Would quickly become a mess. Maybe, but it'd be Qemu's mess ;-)