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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id b10-20020a05622a020a00b003e65228ef54sm753879qtx.86.2023.04.20.13.52.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Apr 2023 13:52:19 -0700 (PDT) Date: Thu, 20 Apr 2023 16:52:18 -0400 From: Peter Xu To: Anish Moorthy Cc: pbonzini@redhat.com, maz@kernel.org, oliver.upton@linux.dev, seanjc@google.com, jthoughton@google.com, bgardon@google.com, dmatlack@google.com, ricarkol@google.com, axelrasmussen@google.com, kvm@vger.kernel.org, kvmarm@lists.linux.dev Subject: Re: [PATCH v3 07/22] KVM: Annotate -EFAULTs from kvm_vcpu_write_guest_page() Message-ID: References: <20230412213510.1220557-1-amoorthy@google.com> <20230412213510.1220557-8-amoorthy@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230412213510.1220557-8-amoorthy@google.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Apr 12, 2023 at 09:34:55PM +0000, Anish Moorthy wrote: > Implement KVM_CAP_MEMORY_FAULT_INFO for efaults from > kvm_vcpu_write_guest_page() > > Signed-off-by: Anish Moorthy > --- > virt/kvm/kvm_main.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 63b4285d858d1..b29a38af543f0 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3119,8 +3119,11 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, > const void *data, int offset, int len) > { > struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn); > + int ret = __kvm_write_guest_page(vcpu->kvm, slot, gfn, data, offset, len); > > - return __kvm_write_guest_page(vcpu->kvm, slot, gfn, data, offset, len); > + if (ret == -EFAULT) > + kvm_populate_efault_info(vcpu, gfn * PAGE_SIZE + offset, len); > + return ret; > } > EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest_page); Why need to trap this? Is this -EFAULT part of the "scalable userfault" plan or not? My previous memory was one can still leave things like copy_to_user() to go via the userfaults channels which should work in parallel with the new vcpu MEMORY_FAULT exit. But maybe the plan changed? Thanks, -- Peter Xu