diff options
Diffstat (limited to '')
| -rw-r--r-- | debian/patches-rt/0048-mm-highmem-Provide-kmap_local.patch | 207 |
1 files changed, 207 insertions, 0 deletions
diff --git a/debian/patches-rt/0048-mm-highmem-Provide-kmap_local.patch b/debian/patches-rt/0048-mm-highmem-Provide-kmap_local.patch new file mode 100644 index 000000000..aa15ab4ec --- /dev/null +++ b/debian/patches-rt/0048-mm-highmem-Provide-kmap_local.patch @@ -0,0 +1,207 @@ +From 452c4c8536ea017ed0f82287834e7cfa2f751488 Mon Sep 17 00:00:00 2001 +From: Thomas Gleixner <tglx@linutronix.de> +Date: Tue, 3 Nov 2020 10:27:37 +0100 +Subject: [PATCH 048/323] mm/highmem: Provide kmap_local* +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz + +Now that the kmap atomic index is stored in task struct provide a +preemptible variant. On context switch the maps of an outgoing task are +removed and the map of the incoming task are restored. That's obviously +slow, but highmem is slow anyway. + +The kmap_local.*() functions can be invoked from both preemptible and +atomic context. kmap local sections disable migration to keep the resulting +virtual mapping address correct, but disable neither pagefaults nor +preemption. + +A wholesale conversion of kmap_atomic to be fully preemptible is not +possible because some of the usage sites might rely on the preemption +disable for serialization or on the implicit pagefault disable. Needs to be +done on a case by case basis. + +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + include/linux/highmem-internal.h | 48 ++++++++++++++++++++++++++++++++ + include/linux/highmem.h | 43 +++++++++++++++++----------- + mm/highmem.c | 6 ++++ + 3 files changed, 81 insertions(+), 16 deletions(-) + +diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h +index c5a22177db85..1bbe96dc8be6 100644 +--- a/include/linux/highmem-internal.h ++++ b/include/linux/highmem-internal.h +@@ -68,6 +68,26 @@ static inline void kmap_flush_unused(void) + __kmap_flush_unused(); + } + ++static inline void *kmap_local_page(struct page *page) ++{ ++ return __kmap_local_page_prot(page, kmap_prot); ++} ++ ++static inline void *kmap_local_page_prot(struct page *page, pgprot_t prot) ++{ ++ return __kmap_local_page_prot(page, prot); ++} ++ ++static inline void *kmap_local_pfn(unsigned long pfn) ++{ ++ return __kmap_local_pfn_prot(pfn, kmap_prot); ++} ++ ++static inline void __kunmap_local(void *vaddr) ++{ ++ kunmap_local_indexed(vaddr); ++} ++ + static inline void *kmap_atomic_prot(struct page *page, pgprot_t prot) + { + preempt_disable(); +@@ -140,6 +160,28 @@ static inline void kunmap(struct page *page) + #endif + } + ++static inline void *kmap_local_page(struct page *page) ++{ ++ return page_address(page); ++} ++ ++static inline void *kmap_local_page_prot(struct page *page, pgprot_t prot) ++{ ++ return kmap_local_page(page); ++} ++ ++static inline void *kmap_local_pfn(unsigned long pfn) ++{ ++ return kmap_local_page(pfn_to_page(pfn)); ++} ++ ++static inline void __kunmap_local(void *addr) ++{ ++#ifdef ARCH_HAS_FLUSH_ON_KUNMAP ++ kunmap_flush_on_unmap(addr); ++#endif ++} ++ + static inline void *kmap_atomic(struct page *page) + { + preempt_disable(); +@@ -181,4 +223,10 @@ do { \ + __kunmap_atomic(__addr); \ + } while (0) + ++#define kunmap_local(__addr) \ ++do { \ ++ BUILD_BUG_ON(__same_type((__addr), struct page *)); \ ++ __kunmap_local(__addr); \ ++} while (0) ++ + #endif +diff --git a/include/linux/highmem.h b/include/linux/highmem.h +index 5c888525b4c5..7a3c6d4b79d8 100644 +--- a/include/linux/highmem.h ++++ b/include/linux/highmem.h +@@ -60,24 +60,22 @@ static inline struct page *kmap_to_page(void *addr); + static inline void kmap_flush_unused(void); + + /** +- * kmap_atomic - Atomically map a page for temporary usage ++ * kmap_local_page - Map a page for temporary usage + * @page: Pointer to the page to be mapped + * + * Returns: The virtual address of the mapping + * +- * Side effect: On return pagefaults and preemption are disabled. +- * + * Can be invoked from any context. + * + * Requires careful handling when nesting multiple mappings because the map + * management is stack based. The unmap has to be in the reverse order of + * the map operation: + * +- * addr1 = kmap_atomic(page1); +- * addr2 = kmap_atomic(page2); ++ * addr1 = kmap_local_page(page1); ++ * addr2 = kmap_local_page(page2); + * ... +- * kunmap_atomic(addr2); +- * kunmap_atomic(addr1); ++ * kunmap_local(addr2); ++ * kunmap_local(addr1); + * + * Unmapping addr1 before addr2 is invalid and causes malfunction. + * +@@ -88,10 +86,26 @@ static inline void kmap_flush_unused(void); + * virtual address of the direct mapping. Only real highmem pages are + * temporarily mapped. + * +- * While it is significantly faster than kmap() it comes with restrictions +- * about the pointer validity and the side effects of disabling page faults +- * and preemption. Use it only when absolutely necessary, e.g. from non +- * preemptible contexts. ++ * While it is significantly faster than kmap() for the higmem case it ++ * comes with restrictions about the pointer validity. Only use when really ++ * necessary. ++ * ++ * On HIGHMEM enabled systems mapping a highmem page has the side effect of ++ * disabling migration in order to keep the virtual address stable across ++ * preemption. No caller of kmap_local_page() can rely on this side effect. ++ */ ++static inline void *kmap_local_page(struct page *page); ++ ++/** ++ * kmap_atomic - Atomically map a page for temporary usage - Deprecated! ++ * @page: Pointer to the page to be mapped ++ * ++ * Returns: The virtual address of the mapping ++ * ++ * Effectively a wrapper around kmap_local_page() which disables pagefaults ++ * and preemption. ++ * ++ * Do not use in new code. Use kmap_local_page() instead. + */ + static inline void *kmap_atomic(struct page *page); + +@@ -101,12 +115,9 @@ static inline void *kmap_atomic(struct page *page); + * + * Counterpart to kmap_atomic(). + * +- * Undoes the side effects of kmap_atomic(), i.e. reenabling pagefaults and ++ * Effectively a wrapper around kunmap_local() which additionally undoes ++ * the side effects of kmap_atomic(), i.e. reenabling pagefaults and + * preemption. +- * +- * Other than that a NOOP for CONFIG_HIGHMEM=n and for mappings of pages +- * in the low memory area. For real highmen pages the mapping which was +- * established with kmap_atomic() is destroyed. + */ + + /* Highmem related interfaces for management code */ +diff --git a/mm/highmem.c b/mm/highmem.c +index d7a1c80001d0..8db577e5290c 100644 +--- a/mm/highmem.c ++++ b/mm/highmem.c +@@ -450,6 +450,11 @@ void *__kmap_local_pfn_prot(unsigned long pfn, pgprot_t prot) + unsigned long vaddr; + int idx; + ++ /* ++ * Disable migration so resulting virtual address is stable ++ * accross preemption. ++ */ ++ migrate_disable(); + preempt_disable(); + idx = arch_kmap_local_map_idx(kmap_local_idx_push(), pfn); + vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx); +@@ -505,6 +510,7 @@ void kunmap_local_indexed(void *vaddr) + current->kmap_ctrl.pteval[kmap_local_idx()] = __pte(0); + kmap_local_idx_pop(); + preempt_enable(); ++ migrate_enable(); + } + EXPORT_SYMBOL(kunmap_local_indexed); + +-- +2.43.0 + |