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[88.21.202.17]) by smtp.gmail.com with ESMTPSA id g6sm17164529wrp.75.2020.05.18.09.06.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 May 2020 09:06:46 -0700 (PDT) Subject: Re: [RFC PATCH v2 6/7] accel/kvm: Let KVM_EXIT_MMIO return error To: Peter Maydell Cc: Paolo Bonzini , qemu-arm , QEMU Developers , kvm-devel , Richard Henderson References: <20200518155308.15851-1-f4bug@amsat.org> <20200518155308.15851-7-f4bug@amsat.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Mon, 18 May 2020 18:06:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 5/18/20 6:01 PM, Peter Maydell wrote: > On Mon, 18 May 2020 at 16:53, Philippe Mathieu-Daudé wrote: >> >> Give the hypervisor a possibility to catch any error >> occuring during KVM_EXIT_MMIO. >> >> Signed-off-by: Philippe Mathieu-Daudé >> --- >> RFC because maybe we simply want to ignore this error instead > > The "right" answer is that the kernel should enhance the KVM_EXIT_MMIO > API to allow userspace to say "sorry, you got a bus error on that > memory access the guest just tried" (which the kernel then has to > turn into an appropriate guest exception, or ignore, depending on > what the architecture requires.) You don't want to set ret to > non-zero here, because that will cause us to VM_STOP, and I > suspect that x86 at least is relying on the implict RAZ/WI > behaviour it currently gets. OK, similar to the worst case I expected here. Thank you for the clear explanation :) > > thanks > -- PMM >