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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.googlemail.com with ESMTPSA id a26sm7524301wmb.37.2022.01.20.05.13.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Jan 2022 05:13:12 -0800 (PST) Message-ID: Date: Thu, 20 Jan 2022 14:13:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH v2 5/7] kvm/riscv: rework guest entry logic Content-Language: en-US To: Mark Rutland , palmer@dabbelt.com Cc: linux-kernel@vger.kernel.org, aleksandar.qemu.devel@gmail.com, alexandru.elisei@arm.com, anup.patel@wdc.com, aou@eecs.berkeley.edu, atish.patra@wdc.com, borntraeger@linux.ibm.com, bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org, dave.hansen@linux.intel.com, frankja@linux.ibm.com, frederic@kernel.org, gor@linux.ibm.com, hca@linux.ibm.com, james.morse@arm.com, jmattson@google.com, joro@8bytes.org, luto@kernel.org, maz@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, nsaenzju@redhat.com, paulmck@kernel.org, paul.walmsley@sifive.com, peterz@infradead.org, seanjc@google.com, suzuki.poulose@arm.com, svens@linux.ibm.com, tglx@linutronix.de, tsbogend@alpha.franken.de, vkuznets@redhat.com, wanpengli@tencent.com, will@kernel.org References: <20220119105854.3160683-1-mark.rutland@arm.com> <20220119105854.3160683-6-mark.rutland@arm.com> <771780a3-39a7-f87e-4b5b-45cf95b3896a@redhat.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/20/22 13:56, Mark Rutland wrote: >> This should be the required architectural behavior: "a CSR access is >> performed after the execution of any prior instructions in program order >> whose behavior modifies or is modified by the CSR state and before the >> execution of any subsequent instructions in program order whose behavior >> modifies or is modified by the CSR state" (Zicsr spec, paragraph "CSR Access >> Ordering", available at >> https://www.five-embeddev.com/riscv-isa-manual/latest/csr.html#csrinsts). > > I think that's necessary, but not sufficient. > > IIUC that wording means that writes to the CSR state occur in program order > without requiring additional barriers to take effect. The current value of the > CSR determines whether interrupts *can* be taken, but that doesn't say that > pending interrrupts *must* be taken immediately when unmasked in the CSR. I see. Yeah, my reasoning was that there would be _different_ instructions executed after the CSR write if an interrupt has to be taken, but perhaps that's a bit of a stretch. Paolo