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Sun, 5 Nov 2023 16:32:54 +0000 (UTC) Received: from avogadro.redhat.com (unknown [10.39.192.93]) by smtp.corp.redhat.com (Postfix) with ESMTP id 620112166B26; Sun, 5 Nov 2023 16:32:47 +0000 (UTC) From: Paolo Bonzini 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 Subject: [PATCH 16/34] KVM: x86: "Reset" vcpu->run->exit_reason early in KVM_RUN Date: Sun, 5 Nov 2023 17:30:19 +0100 Message-ID: <20231105163040.14904-17-pbonzini@redhat.com> In-Reply-To: <20231105163040.14904-1-pbonzini@redhat.com> References: <20231105163040.14904-1-pbonzini@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Chao Peng , linux-riscv@lists.infradead.org, Isaku Yamahata , Xiaoyao Li , Wang , Fuad Tabba , linux-arm-kernel@lists.infradead.org, Maciej Szmigiero , Michael Roth , Ackerley Tng , David Matlack , Vlastimil Babka , =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Isaku Yamahata , Quentin Perret , kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, Jarkko Sakkinen , Yu Zhang , "Kirill A. Shutemov" , kvm-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, Liam Merwick , Vishal Annapurve , linuxppc-dev@lists.ozlabs.org, Xu Yilun , Anish Moorthy Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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 (;;) {