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Fri, 10 Oct 2025 15:48:01 +0000 (UTC) Received: from vschneid-thinkpadt14sgen2i.remote.csb (unknown [10.45.224.29]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 98E831800576; Fri, 10 Oct 2025 15:47:46 +0000 (UTC) From: Valentin Schneider To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnaldo Carvalho de Melo , Josh Poimboeuf , Paolo Bonzini , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Sami Tolvanen , "David S. Miller" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Mel Gorman , Andrew Morton , Masahiro Yamada , Han Shen , Rik van Riel , Jann Horn , Dan Carpenter , Oleg Nesterov , Juri Lelli , Clark Williams , Yair Podemsky , Marcelo Tosatti , Daniel Wagner , Petr Tesarik Subject: [RFC PATCH v6 28/29] x86/mm, mm/vmalloc: Defer kernel TLB flush IPIs under CONFIG_COALESCE_TLBI=y Date: Fri, 10 Oct 2025 17:38:38 +0200 Message-ID: <20251010153839.151763-29-vschneid@redhat.com> In-Reply-To: <20251010153839.151763-1-vschneid@redhat.com> References: <20251010153839.151763-1-vschneid@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251010_164812_074588_6CE721D3 X-CRM114-Status: GOOD ( 25.07 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Previous commits have added an unconditional TLB flush right after switching to the kernel CR3 on NOHZ_FULL CPUs, and a software signal to determine whether a CPU has its kernel CR3 loaded. Using these two components, we can now safely defer kernel TLB flush IPIs targeting NOHZ_FULL CPUs executing in userspace (i.e. with the user CR3 loaded). Note that the COALESCE_TLBI config option is introduced in a later commit, when the whole feature is implemented. Signed-off-by: Valentin Schneider --- arch/x86/include/asm/tlbflush.h | 3 +++ arch/x86/mm/tlb.c | 34 ++++++++++++++++++++++++++------- mm/vmalloc.c | 34 ++++++++++++++++++++++++++++----- 3 files changed, 59 insertions(+), 12 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index e39ae95b85072..6d533afd70952 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -321,6 +321,9 @@ extern void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, unsigned long end, unsigned int stride_shift, bool freed_tables); extern void flush_tlb_kernel_range(unsigned long start, unsigned long end); +#ifdef CONFIG_COALESCE_TLBI +extern void flush_tlb_kernel_range_deferrable(unsigned long start, unsigned long end); +#endif static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a) { diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 39f80111e6f17..aa3a83d5eccc2 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include @@ -1509,23 +1510,24 @@ static void do_kernel_range_flush(void *info) flush_tlb_one_kernel(addr); } -static void kernel_tlb_flush_all(struct flush_tlb_info *info) +static void kernel_tlb_flush_all(smp_cond_func_t cond, struct flush_tlb_info *info) { if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) invlpgb_flush_all(); else - on_each_cpu(do_flush_tlb_all, NULL, 1); + on_each_cpu_cond(cond, do_flush_tlb_all, NULL, 1); } -static void kernel_tlb_flush_range(struct flush_tlb_info *info) +static void kernel_tlb_flush_range(smp_cond_func_t cond, struct flush_tlb_info *info) { if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) invlpgb_kernel_range_flush(info); else - on_each_cpu(do_kernel_range_flush, info, 1); + on_each_cpu_cond(cond, do_kernel_range_flush, info, 1); } -void flush_tlb_kernel_range(unsigned long start, unsigned long end) +static inline void +__flush_tlb_kernel_range(smp_cond_func_t cond, unsigned long start, unsigned long end) { struct flush_tlb_info *info; @@ -1535,13 +1537,31 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end) TLB_GENERATION_INVALID); if (info->end == TLB_FLUSH_ALL) - kernel_tlb_flush_all(info); + kernel_tlb_flush_all(cond, info); else - kernel_tlb_flush_range(info); + kernel_tlb_flush_range(cond, info); put_flush_tlb_info(); } +void flush_tlb_kernel_range(unsigned long start, unsigned long end) +{ + __flush_tlb_kernel_range(NULL, start, end); +} + +#ifdef CONFIG_COALESCE_TLBI +static bool flush_tlb_kernel_cond(int cpu, void *info) +{ + return housekeeping_cpu(cpu, HK_TYPE_KERNEL_NOISE) || + per_cpu(kernel_cr3_loaded, cpu); +} + +void flush_tlb_kernel_range_deferrable(unsigned long start, unsigned long end) +{ + __flush_tlb_kernel_range(flush_tlb_kernel_cond, start, end); +} +#endif + /* * This can be used from process context to figure out what the value of * CR3 is without needing to do a (slow) __read_cr3(). diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 5edd536ba9d2a..c42f413a7a693 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -494,6 +494,30 @@ void vunmap_range_noflush(unsigned long start, unsigned long end) __vunmap_range_noflush(start, end); } +#ifdef CONFIG_COALESCE_TLBI +/* + * !!! BIG FAT WARNING !!! + * + * The CPU is free to cache any part of the paging hierarchy it wants at any + * time. It's also free to set accessed and dirty bits at any time, even for + * instructions that may never execute architecturally. + * + * This means that deferring a TLB flush affecting freed page-table-pages (IOW, + * keeping them in a CPU's paging hierarchy cache) is a recipe for disaster. + * + * This isn't a problem for deferral of TLB flushes in vmalloc, because + * page-table-pages used for vmap() mappings are never freed - see how + * __vunmap_range_noflush() walks the whole mapping but only clears the leaf PTEs. + * If this ever changes, TLB flush deferral will cause misery. + */ +void __weak flush_tlb_kernel_range_deferrable(unsigned long start, unsigned long end) +{ + flush_tlb_kernel_range(start, end); +} +#else +#define flush_tlb_kernel_range_deferrable(start, end) flush_tlb_kernel_range(start, end) +#endif + /** * vunmap_range - unmap kernel virtual addresses * @addr: start of the VM area to unmap @@ -507,7 +531,7 @@ void vunmap_range(unsigned long addr, unsigned long end) { flush_cache_vunmap(addr, end); vunmap_range_noflush(addr, end); - flush_tlb_kernel_range(addr, end); + flush_tlb_kernel_range_deferrable(addr, end); } static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr, @@ -2333,7 +2357,7 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end, nr_purge_nodes = cpumask_weight(&purge_nodes); if (nr_purge_nodes > 0) { - flush_tlb_kernel_range(start, end); + flush_tlb_kernel_range_deferrable(start, end); /* One extra worker is per a lazy_max_pages() full set minus one. */ nr_purge_helpers = atomic_long_read(&vmap_lazy_nr) / lazy_max_pages(); @@ -2436,7 +2460,7 @@ static void free_unmap_vmap_area(struct vmap_area *va) flush_cache_vunmap(va->va_start, va->va_end); vunmap_range_noflush(va->va_start, va->va_end); if (debug_pagealloc_enabled_static()) - flush_tlb_kernel_range(va->va_start, va->va_end); + flush_tlb_kernel_range_deferrable(va->va_start, va->va_end); free_vmap_area_noflush(va); } @@ -2884,7 +2908,7 @@ static void vb_free(unsigned long addr, unsigned long size) vunmap_range_noflush(addr, addr + size); if (debug_pagealloc_enabled_static()) - flush_tlb_kernel_range(addr, addr + size); + flush_tlb_kernel_range_deferrable(addr, addr + size); spin_lock(&vb->lock); @@ -2949,7 +2973,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush) free_purged_blocks(&purge_list); if (!__purge_vmap_area_lazy(start, end, false) && flush) - flush_tlb_kernel_range(start, end); + flush_tlb_kernel_range_deferrable(start, end); mutex_unlock(&vmap_purge_lock); } -- 2.51.0