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Peter Anvin" , Sean Christopherson , Wanpeng Li , Jim Mattson Subject: Re: [PATCH RFC 3/6] KVM: x86: interrupt based APF page-ready event delivery Message-ID: <20200430132805.GB40678@xz-x1> References: <20200429093634.1514902-1-vkuznets@redhat.com> <20200429093634.1514902-4-vkuznets@redhat.com> <20200429212708.GA40678@xz-x1> <87v9lhfk7v.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87v9lhfk7v.fsf@vitty.brq.redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 30, 2020 at 10:31:32AM +0200, Vitaly Kuznetsov wrote: > as we need to write to two MSRs to configure the new mechanism ordering > becomes important. If the guest writes to ASYNC_PF_EN first to establish > the shared memory stucture the interrupt in ASYNC_PF2 is not yet set > (and AFAIR '0' is a valid interrupt!) so if an async pf happens > immediately after that we'll be forced to inject INT0 in the guest and > it'll get confused and linkely miss the event. > > We can probably mandate the reverse sequence: guest has to set up > interrupt in ASYNC_PF2 first and then write to ASYNC_PF_EN (with both > bit 0 and bit 3). In that case the additional 'enable' bit in ASYNC_PF2 > seems redundant. This protocol doesn't look too complex for guests to > follow. Yep looks good. We should also update the document too about the fact. Thanks, -- Peter Xu