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X-IronPort-AV: E=McAfee;i="6600,9927,10889"; a="380545620" X-IronPort-AV: E=Sophos;i="6.03,291,1694761200"; d="scan'208";a="380545620" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Nov 2023 00:49:36 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10889"; a="887305217" X-IronPort-AV: E=Sophos;i="6.03,291,1694761200"; d="scan'208";a="887305217" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.93.9.145]) ([10.93.9.145]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Nov 2023 00:49:24 -0800 Message-ID: Date: Fri, 10 Nov 2023 16:49:21 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 16/34] KVM: x86: "Reset" vcpu->run->exit_reason early in KVM_RUN To: Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Sean Christopherson , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , David Matlack , Yu Zhang , Isaku Yamahata , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A. Shutemov" References: <20231105163040.14904-1-pbonzini@redhat.com> <20231105163040.14904-17-pbonzini@redhat.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: <20231105163040.14904-17-pbonzini@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: qdc1txnhyo8xm9pa7bidkdssdfhw4dba X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 5AD0F160002 X-Rspam-User: X-HE-Tag: 1699606178-693883 X-HE-Meta: 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 i4Riljqx WQBF0nb2L/3b9zegrfjuUDVptOoFef1lR0Yb9FEWJLAJFKFY+0++nfEaMUS8tNt7mx5xa0gBbsoZWI33k3mqQK4883cNF6ryjwsuL1zgTqI1MyVPjUPqchvngiiwcICvFoAnlQrfp7na6wE6PP1+BvUvnoWJgCa2nbF6pAxz4GN9dVLmd/Z5U3n0fowzQjzDPVHHLATnH6eXdus4vQ5agKZFHONG4/DsvLb/l7UJW1+gHVq0Ji7XF6pukhxL6lI1XSsquM87jHejyEULfyutjApUcP50pGSin1yyxeMSlVuRoClylutPbSZ1TRXOKRkRphURVxGiWV0Skk/Teo65GXlAffyd+uHJWyd3cmhAq45ciST+Zt0m9BCiik0MH5ZE50Se5W6cePOHxD74o1ot+nDf2BtmZCyGW2oqjmRQ8I3xQpErEfcXtx4AXIQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/6/2023 12:30 AM, Paolo Bonzini wrote: > From: Sean Christopherson > > Initialize run->exit_reason to KVM_EXIT_UNKNOWN early in KVM_RUN to reduce > the probability of exiting to userspace with a stale run->exit_reason that > *appears* to be valid. > > To support fd-based guest memory (guest memory without a corresponding > userspace virtual address), KVM will exit to userspace for various memory > related errors, which userspace *may* be able to resolve, instead of using > e.g. BUS_MCEERR_AR. And in the more distant future, KVM will also likely > utilize the same functionality to let userspace "intercept" and handle > memory faults when the userspace mapping is missing, i.e. when fast gup() > fails. > > Because many of KVM's internal APIs related to guest memory use '0' to > indicate "success, continue on" and not "exit to userspace", reporting > memory faults/errors to userspace will set run->exit_reason and > corresponding fields in the run structure fields in conjunction with a > a non-zero, negative return code, e.g. -EFAULT or -EHWPOISON. And because > KVM already returns -EFAULT in many paths, there's a relatively high > probability that KVM could return -EFAULT without setting run->exit_reason, > in which case reporting KVM_EXIT_UNKNOWN is much better than reporting > whatever exit reason happened to be in the run structure. > > Note, KVM must wait until after run->immediate_exit is serviced to > sanitize run->exit_reason as KVM's ABI is that run->exit_reason is > preserved across KVM_RUN when run->immediate_exit is true. > > Link: https://lore.kernel.org/all/20230908222905.1321305-1-amoorthy@google.com > Link: https://lore.kernel.org/all/ZFFbwOXZ5uI%2Fgdaf@google.com > Signed-off-by: Sean Christopherson > Reviewed-by: Paolo Bonzini > Reviewed-by: Fuad Tabba > Tested-by: Fuad Tabba > Message-Id: <20231027182217.3615211-19-seanjc@google.com> > Signed-off-by: Paolo Bonzini Reviewed-by: Xiaoyao Li > --- > arch/x86/kvm/x86.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 8f9d8939b63b..f661acb01c58 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -11082,6 +11082,7 @@ static int vcpu_run(struct kvm_vcpu *vcpu) > { > int r; > > + vcpu->run->exit_reason = KVM_EXIT_UNKNOWN; > vcpu->arch.l1tf_flush_l1d = true; > > for (;;) {