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AJvYcCWa+CsObYUvdhQ//WeBsWBOz5EbDx/2UiMTw2v/kvaEUrLryWpllGa4bNpJ3SX93z8Fov1ynyzujZ4pw0vFYK6wsrHFVFW9F61vi5e6 X-Gm-Message-State: AOJu0Yy9r5KOego5Thopr5kt6qeJ6rmvTDINgdHqanwORF0W+OjjU/bE p+Zg9qz1MjIRvE9r7vh2aqWPp13kYAzDP9YZkIfauARwTFpqFsDIC72RH17AgMKefHhmZtqLM2+ Ofw== X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a25:160b:0:b0:dc7:7ce9:fb4d with SMTP id 11-20020a25160b000000b00dc77ce9fb4dmr5036ybw.12.1708628776828; Thu, 22 Feb 2024 11:06:16 -0800 (PST) Reply-To: Sean Christopherson Date: Thu, 22 Feb 2024 11:06:08 -0800 In-Reply-To: <20240222190612.2942589-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240222190612.2942589-1-seanjc@google.com> X-Mailer: git-send-email 2.44.0.rc0.258.g7320e95886-goog Message-ID: <20240222190612.2942589-2-seanjc@google.com> Subject: [PATCH 1/5] KVM: Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY From: Sean Christopherson To: Paolo Bonzini , Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Fuad Tabba , Michael Roth , Isaku Yamahata , Yu Zhang , Chao Peng X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1791627338405751104 X-GMAIL-MSGID: 1791627338405751104 Disallow creating read-only memslots that support GUEST_MEMFD, as GUEST_MEMFD is fundamentally incompatible with KVM's semantics for read-only memslots. Read-only memslots allow the userspace VMM to emulate option ROMs by filling the backing memory with readable, executable code and data, while triggering emulated MMIO on writes. GUEST_MEMFD doesn't currently support writes from userspace and KVM doesn't support emulated MMIO on private accesses, i.e. the guest can only ever read zeros, and writes will always be treated as errors. Cc: Fuad Tabba Cc: Michael Roth Cc: Isaku Yamahata Cc: Yu Zhang Cc: Chao Peng Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory") Signed-off-by: Sean Christopherson --- virt/kvm/kvm_main.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index eb0dfcd157f4..0f9f78f4f7cf 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1617,7 +1617,13 @@ static int check_memory_region_flags(struct kvm *kvm, valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES; #ifdef CONFIG_HAVE_KVM_READONLY_MEM - valid_flags |= KVM_MEM_READONLY; + /* + * GUEST_MEMFD is incompatible with read-only memslots, as writes to + * read-only memslots have emulated MMIO, not page fault, semantics, + * and KVM doesn't allow emulated MMIO for private memory. + */ + if (!(mem->flags & KVM_MEM_GUEST_MEMFD)) + valid_flags |= KVM_MEM_READONLY; #endif if (mem->flags & ~valid_flags)