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charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20240813-fix_fencei_optimization-v1-1-2aadc2cdde95@rivosinc.com> References: <20240813-fix_fencei_optimization-v1-0-2aadc2cdde95@rivosinc.com> In-Reply-To: <20240813-fix_fencei_optimization-v1-0-2aadc2cdde95@rivosinc.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Atish Patra , Samuel Holland , Andrea Parri Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Charlie Jenkins X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2610; i=charlie@rivosinc.com; h=from:subject:message-id; bh=/t/KRCtxUOjdtqgOTwia+D8mTRhtgwlB/ao8pdbfRk4=; b=owGbwMvMwCHWx5hUnlvL8Y3xtFoSQ9rup7/rWhQYedOna+rk5cVYabIzHPq1PYq1ouLvNeF79 T+3vDPtKGVhEONgkBVTZOG51sDceke/7Kho2QSYOaxMIEMYuDgFYCIrFjMydCtumP13P4/a0UfS /lsnpKm6PNogaPD0/2RZJhu9+rvqlowMeyPeNHiZbwyV+VN6b/0CuYCoaUmlOQKFl3JKNlncL/N kAwA= X-Developer-Key: i=charlie@rivosinc.com; a=openpgp; fpr=7D834FF11B1D8387E61C776FFB10D1F27D6B1354 The icache will be flushed in switch_to() if force_icache_flush is true, or in flush_icache_deferred() if icache_stale_mask is set. Between setting force_icache_flush to false and calculating the new icache_stale_mask, preemption needs to be disabled. There are two reasons for this: 1. If CPU migration happens between force_icache_flush =3D false, and the icache_stale_mask is set, an icache flush will not be emitted. 2. smp_processor_id() is used in set_icache_stale_mask() to mark the current CPU as not needing another flush since a flush will have happened either by userspace or by the kernel when performing the migration. smp_processor_id() is currently called twice with preemption enabled which causes a race condition. It allows icache_stale_mask to be populated with inconsistent CPU ids. Resolve these two issues by setting the icache_stale_mask before setting force_icache_flush to false, and using get_cpu()/put_cpu() to obtain the smp_processor_id(). Signed-off-by: Charlie Jenkins Fixes: 6b9391b581fd ("riscv: Include riscv_set_icache_flush_ctx prctl") --- arch/riscv/mm/cacheflush.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c index a03c994eed3b..b81672729887 100644 --- a/arch/riscv/mm/cacheflush.c +++ b/arch/riscv/mm/cacheflush.c @@ -158,6 +158,7 @@ void __init riscv_init_cbo_blocksizes(void) #ifdef CONFIG_SMP static void set_icache_stale_mask(void) { + int cpu =3D get_cpu(); cpumask_t *mask; bool stale_cpu; =20 @@ -168,10 +169,11 @@ static void set_icache_stale_mask(void) * concurrently on different harts. */ mask =3D ¤t->mm->context.icache_stale_mask; - stale_cpu =3D cpumask_test_cpu(smp_processor_id(), mask); + stale_cpu =3D cpumask_test_cpu(cpu, mask); =20 cpumask_setall(mask); - cpumask_assign_cpu(smp_processor_id(), mask, stale_cpu); + cpumask_assign_cpu(cpu, mask, stale_cpu); + put_cpu(); } #endif =20 @@ -239,14 +241,12 @@ int riscv_set_icache_flush_ctx(unsigned long ctx, uns= igned long scope) case PR_RISCV_CTX_SW_FENCEI_OFF: switch (scope) { case PR_RISCV_SCOPE_PER_PROCESS: - current->mm->context.force_icache_flush =3D false; - set_icache_stale_mask(); + current->mm->context.force_icache_flush =3D false; break; case PR_RISCV_SCOPE_PER_THREAD: - current->thread.force_icache_flush =3D false; - set_icache_stale_mask(); + current->thread.force_icache_flush =3D false; break; default: return -EINVAL; --=20 2.45.0 From nobody Mon Feb 9 01:11:35 2026 Received: from mail-pl1-f180.google.com (mail-pl1-f180.google.com [209.85.214.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B31FE1AB52F for ; Tue, 13 Aug 2024 23:02:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.180 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723590147; cv=none; b=h7yFmvyjk4BLgenk/9ULi5pfSVVYEweSCBzgr5ylJRt4q1W8e2rQqDBRP7dsbufkggAyTVDw2PYFKO6Y1db48u3g9AmN4s/Xwd+miVyRH51X63eZ6N6qiW6T7yLIf/X5ZaHj3jLuTkPjFVTmpqFYAuFiGkM3Pq+QbUhSsd/SoXA= ARC-Message-Signature: i=1; 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Tue, 13 Aug 2024 16:02:24 -0700 (PDT) From: Charlie Jenkins Date: Tue, 13 Aug 2024 16:02:18 -0700 Subject: [PATCH 2/2] riscv: Eagerly flush in flush_icache_deferred() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20240813-fix_fencei_optimization-v1-2-2aadc2cdde95@rivosinc.com> References: <20240813-fix_fencei_optimization-v1-0-2aadc2cdde95@rivosinc.com> In-Reply-To: <20240813-fix_fencei_optimization-v1-0-2aadc2cdde95@rivosinc.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Atish Patra , Samuel Holland , Andrea Parri Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Charlie Jenkins X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4833; i=charlie@rivosinc.com; h=from:subject:message-id; bh=iv4UBEdbbtayWIGJ+KvTcVQaR/bcv8PC3YtHCe72xsM=; b=owGbwMvMwCHWx5hUnlvL8Y3xtFoSQ9rup791Agy4TQM7zv87HMWkcubQjQDXtw9ml7m/Mvp2R GQy+57IjlIWBjEOBlkxRRaeaw3MrXf0y46Klk2AmcPKBDKEgYtTACaiMo3hr6hzvvqen3NWppxa WSPcr+91yjXDZ8v2u+vfHvIQ8Cu+f5fhf1zKnamvbJ+mys7o0HO+nMAmlxNqNTF4vfGU/3vslDU j2AE= X-Developer-Key: i=charlie@rivosinc.com; a=openpgp; fpr=7D834FF11B1D8387E61C776FFB10D1F27D6B1354 It is possible for mm->context.icache_stale_mask to be set between switch_mm() and switch_to() when there are two threads on different CPUs executing in the same mm: <---- Thread 1 starts running here on CPU1 <---- Thread 2 starts running here with same mm T2: prctl(PR_RISCV_SET_ICACHE_FLUSH_CTX, PR_RISCV_CTX_SW_FENCEI_ON, PR_RISC= V_SCOPE_PER_PROCESS); T2: <-- kernel sets current->mm->context.force_icache_flush to true T2: T2: fence.i T1: fence.i (to synchronize with other thread, has some logic to determine when to do this) T1: <-- thread 1 is preempted T1: <-- thread 1 is placed onto CPU3 and starts context switch sequence T1 (kernel): flush_icache_deferred() -> skips flush because switch_to_shoul= d_flush_icache() returns true -> thread has migrated and task->mm->context.force_icache_flush is= true T2: prctl(PR_RISCV_SET_ICACHE_FLUSH_CTX, PR_RISCV_CTX_SW_FENCEI_OFF, PR_RIS= CV_SCOPE_PER_PROCESS); T2 (kernel): kernel sets current->mm->context.force_icache_flush =3D false T1 (kernel): switch_to() calls switch_to_should_flush_icache() which now returns false because task->mm->context.force_icache_flush is false due to the other thread emitting PR_RISCV_CTX_SW_FENCEI_OFF. T1 (back in userspace): Instruction cache was never flushed on context switch to CPU3, and thus may execute incorrect instructions. This commit fixes this issue by also flushing in switch_to() when task->mm->context.icache_stale_mask is set, and always flushing in flush_icache_deferred(). It is possible for switch_mm() to be called without being followed by switch_to() such as with the riscv efi driver in efi_virtmap_load(), so we cannot do all of the flushing in switch_to(). To avoid flushing multiple times in a single context switch, clear mm->context.icache_stale_mask in switch_mm() and only flush in switch_to() if it was set again in the meantime. Set icache_stale_mask when handling prctl and in switch_to() if task->mm->context.force_icache_flush is set to prepare for next context switch. Signed-off-by: Charlie Jenkins Fixes: 6b9391b581fd ("riscv: Include riscv_set_icache_flush_ctx prctl") --- arch/riscv/include/asm/switch_to.h | 19 ++++++++++++++++--- arch/riscv/mm/cacheflush.c | 1 + arch/riscv/mm/context.c | 6 +----- 3 files changed, 18 insertions(+), 8 deletions(-) diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/sw= itch_to.h index 7594df37cc9f..5701cfcf2b68 100644 --- a/arch/riscv/include/asm/switch_to.h +++ b/arch/riscv/include/asm/switch_to.h @@ -76,11 +76,24 @@ extern struct task_struct *__switch_to(struct task_stru= ct *, static inline bool switch_to_should_flush_icache(struct task_struct *task) { #ifdef CONFIG_SMP - bool stale_mm =3D task->mm && task->mm->context.force_icache_flush; - bool stale_thread =3D task->thread.force_icache_flush; + bool stale_mm =3D false; bool thread_migrated =3D smp_processor_id() !=3D task->thread.prev_cpu; + bool stale_thread =3D thread_migrated && task->thread.force_icache_flush; + + if (task->mm) { + /* + * The mm is only stale if the respective CPU bit in + * icache_stale_mask is set. force_icache_flush indicates that + * icache_stale_mask should be set again before returning to userspace. + */ + stale_mm =3D cpumask_test_cpu(smp_processor_id(), + &task->mm->context.icache_stale_mask); + cpumask_assign_cpu(smp_processor_id(), + &task->mm->context.icache_stale_mask, + task->mm->context.force_icache_flush); + } =20 - return thread_migrated && (stale_mm || stale_thread); + return stale_mm || stale_thread; #else return false; #endif diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c index b81672729887..c4a9ac2ad7ab 100644 --- a/arch/riscv/mm/cacheflush.c +++ b/arch/riscv/mm/cacheflush.c @@ -230,6 +230,7 @@ int riscv_set_icache_flush_ctx(unsigned long ctx, unsig= ned long scope) switch (scope) { case PR_RISCV_SCOPE_PER_PROCESS: current->mm->context.force_icache_flush =3D true; + cpumask_setall(¤t->mm->context.icache_stale_mask); break; case PR_RISCV_SCOPE_PER_THREAD: current->thread.force_icache_flush =3D true; diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c index 4abe3de23225..9e82e2a99441 100644 --- a/arch/riscv/mm/context.c +++ b/arch/riscv/mm/context.c @@ -306,11 +306,7 @@ static inline void flush_icache_deferred(struct mm_str= uct *mm, unsigned int cpu, */ smp_mb(); =20 - /* - * If cache will be flushed in switch_to, no need to flush here. - */ - if (!(task && switch_to_should_flush_icache(task))) - local_flush_icache_all(); + local_flush_icache_all(); } #endif } --=20 2.45.0