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([2001:b07:6468:f312:b509:fc01:ee8a:ca8a]) by smtp.gmail.com with ESMTPSA id m3sm51279088wrs.53.2020.01.21.06.24.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jan 2020 06:24:33 -0800 (PST) Subject: Re: [PATCH 04/14] KVM: Play nice with read-only memslots when querying host page size To: Sean Christopherson Cc: Paul Mackerras , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Andrew Morton , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , kvm-ppc@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, syzbot+c9d1fb51ac9d0d10c39d@syzkaller.appspotmail.com, Andrea Arcangeli , Dan Williams , Barret Rhoden , David Hildenbrand , Jason Zeng , Dave Jiang , Liran Alon , linux-nvdimm References: <20200108202448.9669-1-sean.j.christopherson@intel.com> <20200108202448.9669-5-sean.j.christopherson@intel.com> From: Paolo Bonzini Message-ID: <2c091d40-8e32-1e55-2eff-27a4b43e0674@redhat.com> Date: Tue, 21 Jan 2020 15:24:29 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20200108202448.9669-5-sean.j.christopherson@intel.com> Content-Language: en-US X-MC-Unique: v6v3HiQMOnm3LK755P1hXQ-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit 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: On 08/01/20 21:24, Sean Christopherson wrote: > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 5f7f06824c2b..d9aced677ddd 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -1418,15 +1418,23 @@ EXPORT_SYMBOL_GPL(kvm_is_visible_gfn); > > unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn) > { > + struct kvm_memory_slot *slot; > struct vm_area_struct *vma; > unsigned long addr, size; > > size = PAGE_SIZE; > > - addr = kvm_vcpu_gfn_to_hva(vcpu, gfn); > - if (kvm_is_error_hva(addr)) > + /* > + * Manually do the equivalent of kvm_vcpu_gfn_to_hva() to avoid the > + * "writable" check in __gfn_to_hva_many(), which will always fail on > + * read-only memslots due to gfn_to_hva() assuming writes. > + */ > + slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn); > + if (!slot || slot->flags & KVM_MEMSLOT_INVALID) > return PAGE_SIZE; > > + addr = __gfn_to_hva_memslot(slot, gfn); > + > down_read(¤t->mm->mmap_sem); > vma = find_vma(current->mm, addr); > if (!vma) > Even simpler: use kvm_vcpu_gfn_to_hva_prot - addr = kvm_vcpu_gfn_to_hva(vcpu, gfn); + addr = kvm_vcpu_gfn_to_hva_prot(vcpu, gfn, NULL); "You are in a maze of twisty little functions, all alike". Paolo