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[93.34.153.63]) by smtp.gmail.com with ESMTPSA id l8sm5098420wrg.40.2019.06.27.09.19.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Jun 2019 09:19:59 -0700 (PDT) To: Dave Martin , Andrew Jones References: <20190621163422.6127-1-drjones@redhat.com> <20190621163422.6127-8-drjones@redhat.com> <20190627104638.x4gxsmv7vpww3mra@kamzik.brq.redhat.com> <20190627114701.n7tjgmljeribk7to@kamzik.brq.redhat.com> <20190627151628.GI2790@e103592.cambridge.arm.com> From: Richard Henderson Openpgp: preference=signencrypt Message-ID: Date: Thu, 27 Jun 2019 18:19:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190627151628.GI2790@e103592.cambridge.arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2a00:1450:4864:20::444 Subject: Re: [Qemu-devel] [PATCH v2 07/14] target/arm/cpu64: max cpu: Introduce sve properties X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "peter.maydell@linaro.org" , "qemu-devel@nongnu.org" , "armbru@redhat.com" , Auger Eric , "qemu-arm@nongnu.org" , "imammedo@redhat.com" , "alex.bennee@linaro.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/27/19 5:16 PM, Dave Martin wrote: > The architecture says: > > "For all purposes other than returning the result of a direct read of > ZCR_EL1 then this field behaves as if it is set to the minimum of the > stored value and the constrained length inherited from more privileged > Exception levels in the current Security state, rounded down to the > nearest implemented vector length." > > I think the behaviour of a direct read is implied: the LEN bits yielded > by an MRS should contain exactly what was last written to them via MSR. I agree. Moreover, the value written to ZCR_ELx.LEN should not be directly adjusted because the effective value also depends on ZCR_EL(x+1).LEN, and if the higher-level EL register changes, the lower-level EL must see the effect. The function that should be modified instead is sve_zcr_len_for_el(). r~