Messages in this thread Patch in this message | | | From | ira.weiny@intel ... | Subject | [PATCH V8 41/44] kmap: Ensure kmap works for devmap pages | Date | Thu, 27 Jan 2022 09:55:02 -0800 |
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From: Ira Weiny <ira.weiny@intel.com>
Users of devmap pages should not have to know that the pages they are operating on are special.
Co-opt the kmap_{local_page,atomic}() to mediate access to PKS protected pages via the devmap facility. kmap_{local_page,atomic}() are both thread local mappings so they work well with the thread specific protections available.
kmap(), on the other hand, allows for global mappings to be established, Which is incompatible with the underlying PKS facility. For this reason kmap() is not supported. Rather than leave the kmap mappings to fault at random times when users may access them, call pgmap_protection_flag_invalid() to show kmap() users the call stack of where mapping was created. This allows better debugging.
This behavior is safe because neither of the 2 current DAX-capable filesystems (ext4 and xfs) perform such global mappings. And known device drivers that would handle devmap pages are not using kmap(). Any future filesystems that gain DAX support, or device drivers wanting to support devmap protected pages will need to use kmap_local_page().
Direct-map exposure is already mitigated by default on HIGHMEM systems because by definition HIGHMEM systems do not have large capacities of memory in the direct map. And using kmap in those systems actually creates a separate mapping. Therefore, to reduce complexity HIGHMEM systems are not supported.
Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
--- Changes for V8 Reword commit message --- include/linux/highmem-internal.h | 5 +++++ mm/Kconfig | 1 + 2 files changed, 6 insertions(+)
diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h index 0a0b2b09b1b8..1a006558734c 100644 --- a/include/linux/highmem-internal.h +++ b/include/linux/highmem-internal.h @@ -159,6 +159,7 @@ static inline struct page *kmap_to_page(void *addr) static inline void *kmap(struct page *page) { might_sleep(); + pgmap_protection_flag_invalid(page); return page_address(page); } @@ -174,6 +175,7 @@ static inline void kunmap(struct page *page) static inline void *kmap_local_page(struct page *page) { + pgmap_mk_readwrite(page); return page_address(page); } @@ -197,6 +199,7 @@ static inline void __kunmap_local(void *addr) #ifdef ARCH_HAS_FLUSH_ON_KUNMAP kunmap_flush_on_unmap(addr); #endif + pgmap_mk_noaccess(kmap_to_page(addr)); } static inline void *kmap_atomic(struct page *page) @@ -206,6 +209,7 @@ static inline void *kmap_atomic(struct page *page) else preempt_disable(); pagefault_disable(); + pgmap_mk_readwrite(page); return page_address(page); } @@ -224,6 +228,7 @@ static inline void __kunmap_atomic(void *addr) #ifdef ARCH_HAS_FLUSH_ON_KUNMAP kunmap_flush_on_unmap(addr); #endif + pgmap_mk_noaccess(kmap_to_page(addr)); pagefault_enable(); if (IS_ENABLED(CONFIG_PREEMPT_RT)) migrate_enable(); diff --git a/mm/Kconfig b/mm/Kconfig index 67e0264acf7d..d537679448ae 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -779,6 +779,7 @@ config ZONE_DEVICE config DEVMAP_ACCESS_PROTECTION bool "Access protection for memremap_pages()" depends on NVDIMM_PFN + depends on !HIGHMEM depends on ARCH_HAS_SUPERVISOR_PKEYS select ARCH_ENABLE_SUPERVISOR_PKEYS default y -- 2.31.1
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