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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id f5sm11154367edj.1.2020.05.23.09.34.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 May 2020 09:34:18 -0700 (PDT) From: Vitaly Kuznetsov To: Vivek Goyal Cc: kvm@vger.kernel.org, x86@kernel.org, Paolo Bonzini , Andy Lutomirski , Thomas Gleixner , Borislav Petkov , "H. Peter Anvin" , Wanpeng Li , Sean Christopherson , Jim Mattson , Gavin Shan , Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/8] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info In-Reply-To: <20200521183832.GB46035@redhat.com> References: <20200511164752.2158645-1-vkuznets@redhat.com> <20200511164752.2158645-3-vkuznets@redhat.com> <20200521183832.GB46035@redhat.com> Date: Sat, 23 May 2020 18:34:17 +0200 Message-ID: <87sgfq8vau.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Vivek Goyal writes: > On Mon, May 11, 2020 at 06:47:46PM +0200, Vitaly Kuznetsov wrote: >> Currently, APF mechanism relies on the #PF abuse where the token is being >> passed through CR2. If we switch to using interrupts to deliver page-ready >> notifications we need a different way to pass the data. Extent the existing >> 'struct kvm_vcpu_pv_apf_data' with token information for page-ready >> notifications. >> >> The newly introduced apf_put_user_ready() temporary puts both reason >> and token information, this will be changed to put token only when we >> switch to interrupt based notifications. >> >> Signed-off-by: Vitaly Kuznetsov >> --- >> arch/x86/include/uapi/asm/kvm_para.h | 3 ++- >> arch/x86/kvm/x86.c | 17 +++++++++++++---- >> 2 files changed, 15 insertions(+), 5 deletions(-) >> >> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h >> index 2a8e0b6b9805..e3602a1de136 100644 >> --- a/arch/x86/include/uapi/asm/kvm_para.h >> +++ b/arch/x86/include/uapi/asm/kvm_para.h >> @@ -113,7 +113,8 @@ struct kvm_mmu_op_release_pt { >> >> struct kvm_vcpu_pv_apf_data { >> __u32 reason; > > Hi Vitaly, > > Given we are redoing it, can we convert "reason" into a flag instead > and use bit 0 for signalling "page not present" Then rest of the 31 > bits can be used for other purposes. I potentially want to use one bit to > signal error (if it is known at the time of injecting #PF). Yes, I think we can do that. The existing KVM_PV_REASON_PAGE_READY and KVM_PV_REASON_PAGE_NOT_PRESENT are mutually exclusive and can be converted to flags (we'll only have KVM_PV_REASON_PAGE_NOT_PRESENT in use when this series is merged). > >> - __u8 pad[60]; >> + __u32 pageready_token; >> + __u8 pad[56]; > > Given token is 32 bit, for returning error in "page ready" type messages, > I will probably use padding bytes and create pagready_flag and use one > of the bits to signal error. In case we're intended to pass more data in synchronous notifications, shall we leave some blank space after 'flags' ('reason' previously) and before 'token'? -- Vitaly