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([71.212.131.115]) by smtp.gmail.com with ESMTPSA id u9-20020a63a909000000b005633311c70dsm4226472pge.32.2023.08.26.16.24.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 26 Aug 2023 16:24:19 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Cc: peter.maydell@linaro.org, pbonzini@redhat.com, alex.bennee@linaro.org Subject: [PATCH 2/3] softmmu: Use async_run_on_cpu in tcg_commit Date: Sat, 26 Aug 2023 16:24:14 -0700 Message-Id: <20230826232415.80233-3-richard.henderson@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230826232415.80233-1-richard.henderson@linaro.org> References: <20230826232415.80233-1-richard.henderson@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::22b; envelope-from=richard.henderson@linaro.org; helo=mail-oi1-x22b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org After system startup, run the update to memory_dispatch and the tlb_flush on the cpu. This eliminates a race, wherein a running cpu sees the memory_dispatch change but has not yet seen the tlb_flush. Since the update now happens on the cpu, we need not use qatomic_rcu_read to protect the read of memory_dispatch. Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1826 Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1834 Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1846 Signed-off-by: Richard Henderson Tested-by: Alex Bennée Reviewed-by: Alex Bennée --- softmmu/physmem.c | 40 +++++++++++++++++++++++++++++----------- 1 file changed, 29 insertions(+), 11 deletions(-) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index 7597dc1c39..18277ddd67 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -680,8 +680,7 @@ address_space_translate_for_iotlb(CPUState *cpu, int asidx, hwaddr orig_addr, IOMMUTLBEntry iotlb; int iommu_idx; hwaddr addr = orig_addr; - AddressSpaceDispatch *d = - qatomic_rcu_read(&cpu->cpu_ases[asidx].memory_dispatch); + AddressSpaceDispatch *d = cpu->cpu_ases[asidx].memory_dispatch; for (;;) { section = address_space_translate_internal(d, addr, &addr, plen, false); @@ -2412,7 +2411,7 @@ MemoryRegionSection *iotlb_to_section(CPUState *cpu, { int asidx = cpu_asidx_from_attrs(cpu, attrs); CPUAddressSpace *cpuas = &cpu->cpu_ases[asidx]; - AddressSpaceDispatch *d = qatomic_rcu_read(&cpuas->memory_dispatch); + AddressSpaceDispatch *d = cpuas->memory_dispatch; int section_index = index & ~TARGET_PAGE_MASK; MemoryRegionSection *ret; @@ -2487,23 +2486,42 @@ static void tcg_log_global_after_sync(MemoryListener *listener) } } +static void tcg_commit_cpu(CPUState *cpu, run_on_cpu_data data) +{ + CPUAddressSpace *cpuas = data.host_ptr; + + cpuas->memory_dispatch = address_space_to_dispatch(cpuas->as); + tlb_flush(cpu); +} + static void tcg_commit(MemoryListener *listener) { CPUAddressSpace *cpuas; - AddressSpaceDispatch *d; + CPUState *cpu; assert(tcg_enabled()); /* since each CPU stores ram addresses in its TLB cache, we must reset the modified entries */ cpuas = container_of(listener, CPUAddressSpace, tcg_as_listener); - cpu_reloading_memory_map(); - /* The CPU and TLB are protected by the iothread lock. - * We reload the dispatch pointer now because cpu_reloading_memory_map() - * may have split the RCU critical section. + cpu = cpuas->cpu; + + /* + * Defer changes to as->memory_dispatch until the cpu is quiescent. + * Otherwise we race between (1) other cpu threads and (2) ongoing + * i/o for the current cpu thread, with data cached by mmu_lookup(). + * + * In addition, queueing the work function will kick the cpu back to + * the main loop, which will end the RCU critical section and reclaim + * the memory data structures. + * + * That said, the listener is also called during realize, before + * all of the tcg machinery for run-on is initialized: thus halt_cond. */ - d = address_space_to_dispatch(cpuas->as); - qatomic_rcu_set(&cpuas->memory_dispatch, d); - tlb_flush(cpuas->cpu); + if (cpu->halt_cond) { + async_run_on_cpu(cpu, tcg_commit_cpu, RUN_ON_CPU_HOST_PTR(cpuas)); + } else { + tcg_commit_cpu(cpu, RUN_ON_CPU_HOST_PTR(cpuas)); + } } static void memory_map_init(void)