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Wed, 28 Jul 2021 10:21:55 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1m8ghF-001VRt-94; Wed, 28 Jul 2021 11:21:53 +0100 Date: Wed, 28 Jul 2021 11:21:52 +0100 Message-ID: <87y29qd9hb.wl-maz@kernel.org> From: Marc Zyngier To: Will Deacon Subject: Re: [PATCH 05/16] KVM: arm64: Plumb MMIO checking into the fault handling In-Reply-To: <20210727181120.GD19173@willie-the-truck> References: <20210715163159.1480168-1-maz@kernel.org> <20210715163159.1480168-6-maz@kernel.org> <20210727181120.GD19173@willie-the-truck> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qperret@google.com, dbrazdil@google.com, vatsa@codeaurora.org, sdonthineni@nvidia.com, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: kvm@vger.kernel.org, kernel-team@android.com, Srivatsa Vaddagiri , linux-kernel@vger.kernel.org, Shanker R Donthineni , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Tue, 27 Jul 2021 19:11:21 +0100, Will Deacon wrote: > > On Thu, Jul 15, 2021 at 05:31:48PM +0100, Marc Zyngier wrote: > > Plumb the MMIO checking code into the MMIO fault handling code. > > Nothing allows a region to be registered yet, so there should be > > no funtional change either. > > Typo: functional > > > Signed-off-by: Marc Zyngier > > --- > > arch/arm64/kvm/mmio.c | 10 ++++++++++ > > 1 file changed, 10 insertions(+) > > > > diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c > > index 3dd38a151d2a..fd5747279d27 100644 > > --- a/arch/arm64/kvm/mmio.c > > +++ b/arch/arm64/kvm/mmio.c > > @@ -6,6 +6,7 @@ > > > > #include > > #include > > +#include > > #include > > > > #include "trace.h" > > @@ -130,6 +131,10 @@ int io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa) > > int len; > > u8 data_buf[8]; > > > > + /* Check failed? Return to the guest for debriefing... */ > > + if (!kvm_check_ioguard_page(vcpu, fault_ipa)) > > + return 1; > > + > > /* > > * No valid syndrome? Ask userspace for help if it has > > * volunteered to do so, and bail out otherwise. > > @@ -156,6 +161,11 @@ int io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa) > > len = kvm_vcpu_dabt_get_as(vcpu); > > rt = kvm_vcpu_dabt_get_rd(vcpu); > > > > + /* If we cross a page boundary, check that too... */ > > + if (((fault_ipa + len - 1) & PAGE_MASK) != (fault_ipa & PAGE_MASK) && > > + !kvm_check_ioguard_page(vcpu, fault_ipa + len - 1)) > > + return 1; > > + > > I find this a little odd as the checks straddle the invalid syndrome check, > meaning that the relative priorities of KVM_ARCH_FLAG_MMIO_GUARD and > KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER are unclear. Good point. And the combination of both flags on its own is odd. Maybe KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER should be ignored or deemed incompatible with the MMIO guard feature. The lack of syndrome information means that we cannot really test for the boundaries of the access (len is invalid), so I'd be tempted to inject an abort in this case. Thoughts? M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm