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(cst-prg-92-82.cust.vodafone.cz. [46.135.92.82]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43d8fba4b4fsm161194865e9.1.2025.04.01.07.35.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Apr 2025 07:35:30 -0700 (PDT) From: Mateusz Guzik To: dave.hansen@linux.intel.com Cc: linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org, Mateusz Guzik Subject: [PATCH] x86/mm: stop prefetching the mmap semaphore on page faults Date: Tue, 1 Apr 2025 16:35:20 +0200 Message-ID: <20250401143520.1113572-1-mjguzik@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The prefetchw dates back decades and the fundamental notion of doing something like this on a lock is shady. Moreover, for few years now in the fast path faults are handled with RCU + per-vma locking, hopefully not even looking at the lock to begin with. As such just remove it. I did not see a point benchmarking this. Given that it is not expected to be looked at by default justifies not doing the prefetch. Signed-off-by: Mateusz Guzik Acked-by: David Hildenbrand --- arch/x86/mm/fault.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 296d294142c8..697432f63c59 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -13,7 +13,6 @@ #include /* kmmio_handler, ... */ #include /* perf_sw_event */ #include /* hstate_index_to_shift */ -#include /* prefetchw */ #include /* exception_enter(), ... */ #include /* faulthandler_disabled() */ #include /* efi_crash_gracefully_on_page_fault()*/ @@ -1496,8 +1495,6 @@ DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault) =20 address =3D cpu_feature_enabled(X86_FEATURE_FRED) ? fred_event_data(regs)= : read_cr2(); =20 - prefetchw(¤t->mm->mmap_lock); - /* * KVM uses #PF vector to deliver 'page not present' events to guests * (asynchronous page fault mechanism). The event happens when a --=20 2.43.0