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From: ira.weiny@intel.com
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Subject: [PATCH RFC PKS/PMEM 05/58] kmap: Introduce k[un]map_thread
Date: Fri,  9 Oct 2020 12:49:40 -0700
Message-ID: <20201009195033.3208459-6-ira.weiny@intel.com> (raw)
In-Reply-To: <20201009195033.3208459-1-ira.weiny@intel.com>

From: Ira Weiny <ira.weiny@intel.com>

To correctly support the semantics of kmap() with Kernel protection keys
(PKS), kmap() may be required to set the protections on multiple
processors (globally).  Enabling PKS globally can be very expensive
depending on the requested operation.  Furthermore, enabling a domain
globally reduces the protection afforded by PKS.

Most kmap() (Aprox 209 of 229) callers use the map within a single thread and
have no need for the protection domain to be enabled globally.  However, the
remaining callers do not follow this pattern and, as best I can tell, expect
the mapping to be 'global' and available to any thread who may access the
mapping.[1]

We don't anticipate global mappings to pmem, however in general there is a
danger in changing the semantics of kmap().  Effectively, this would cause an
unresolved page fault with little to no information about why the failure
occurred.

To resolve this a number of options were considered.

1) Attempt to change all the thread local kmap() calls to kmap_atomic()[2]
2) Introduce a flags parameter to kmap() to indicate if the mapping should be
   global or not
3) Change ~20 call sites to 'kmap_global()' to indicate that they require a
   global enablement of the pages.
4) Change ~209 call sites to 'kmap_thread()' to indicate that the mapping is to
   be used within that thread of execution only

Option 1 is simply not feasible.  Option 2 would require all of the call sites
of kmap() to change.  Option 3 seems like a good minimal change but there is a
danger that new code may miss the semantic change of kmap() and not get the
behavior the developer intended.  Therefore, #4 was chosen.

Subsequent patches will convert most ~90% of the kmap callers to this new call
leaving about 10% of the existing kmap callers to enable PKS globally.

Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
 include/linux/highmem.h | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 2a9806e3b8d2..ef7813544719 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -60,7 +60,7 @@ static inline void kmap_flush_tlb(unsigned long addr) { }
 #endif
 
 void *kmap_high(struct page *page);
-static inline void *kmap(struct page *page)
+static inline void *__kmap(struct page *page, bool global)
 {
 	void *addr;
 
@@ -74,20 +74,20 @@ static inline void *kmap(struct page *page)
 	 * Even non-highmem pages may have additional access protections which
 	 * need to be checked and potentially enabled.
 	 */
-	dev_page_enable_access(page, true);
+	dev_page_enable_access(page, global);
 	return addr;
 }
 
 void kunmap_high(struct page *page);
 
-static inline void kunmap(struct page *page)
+static inline void __kunmap(struct page *page, bool global)
 {
 	might_sleep();
 	/*
 	 * Even non-highmem pages may have additional access protections which
 	 * need to be checked and potentially disabled.
 	 */
-	dev_page_disable_access(page, true);
+	dev_page_disable_access(page, global);
 	if (!PageHighMem(page))
 		return;
 	kunmap_high(page);
@@ -160,10 +160,10 @@ static inline struct page *kmap_to_page(void *addr)
 
 static inline unsigned long totalhigh_pages(void) { return 0UL; }
 
-static inline void *kmap(struct page *page)
+static inline void *__kmap(struct page *page, bool global)
 {
 	might_sleep();
-	dev_page_enable_access(page, true);
+	dev_page_enable_access(page, global);
 	return page_address(page);
 }
 
@@ -171,9 +171,9 @@ static inline void kunmap_high(struct page *page)
 {
 }
 
-static inline void kunmap(struct page *page)
+static inline void __kunmap(struct page *page, bool global)
 {
-	dev_page_disable_access(page, true);
+	dev_page_disable_access(page, global);
 #ifdef ARCH_HAS_FLUSH_ON_KUNMAP
 	kunmap_flush_on_unmap(page_address(page));
 #endif
@@ -238,6 +238,24 @@ static inline void kmap_atomic_idx_pop(void)
 
 #endif
 
+static inline void *kmap(struct page *page)
+{
+	return __kmap(page, true);
+}
+static inline void kunmap(struct page *page)
+{
+	__kunmap(page, true);
+}
+
+static inline void *kmap_thread(struct page *page)
+{
+	return __kmap(page, false);
+}
+static inline void kunmap_thread(struct page *page)
+{
+	__kunmap(page, false);
+}
+
 /*
  * Prevent people trying to call kunmap_atomic() as if it were kunmap()
  * kunmap_atomic() should get the return value of kmap_atomic, not the page.
-- 
2.28.0.rc0.12.gb6a658bd00c9


  parent reply index

Thread overview: 93+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-09 19:49 [PATCH RFC PKS/PMEM 00/58] PMEM: Introduce stray write protection for PMEM ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 01/58] x86/pks: Add a global pkrs option ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 02/58] x86/pks/test: Add testing for global option ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 03/58] memremap: Add zone device access protection ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 04/58] kmap: Add stray access protection for device pages ira.weiny
2020-10-09 19:49 ` ira.weiny [this message]
2020-11-10  1:13   ` [PATCH RFC PKS/PMEM 05/58] kmap: Introduce k[un]map_thread Thomas Gleixner
2020-11-10  4:59     ` Ira Weiny
2020-11-10  8:48       ` Thomas Gleixner
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 06/58] kmap: Introduce k[un]map_thread debugging ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 07/58] drivers/drbd: Utilize new kmap_thread() ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 08/58] drivers/firmware_loader: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 09/58] drivers/gpu: " ira.weiny
2020-10-09 22:03   ` Daniel Vetter
2020-10-10 23:01     ` Ira Weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 10/58] drivers/rdma: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 11/58] drivers/net: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 12/58] fs/afs: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 13/58] fs/btrfs: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 14/58] fs/cifs: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 15/58] fs/ecryptfs: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 16/58] fs/gfs2: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 17/58] fs/nilfs2: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 18/58] fs/hfs: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 19/58] fs/hfsplus: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 20/58] fs/jffs2: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 21/58] fs/nfs: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 22/58] fs/f2fs: " ira.weiny
2020-10-09 21:34   ` Eric Biggers
2020-10-10  0:39     ` Matthew Wilcox
2020-10-10  1:30       ` Eric Biggers
2020-10-12  6:56         ` Ira Weiny
2020-10-12 16:19           ` Eric Biggers
2020-10-12 16:28             ` Dave Hansen
2020-10-12 16:44               ` Matthew Wilcox
2020-10-12 19:53                 ` Ira Weiny
2020-10-12 20:02                   ` Matthew Wilcox
2020-10-12 23:31                     ` Ira Weiny
2020-10-10  2:43     ` James Bottomley
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 23/58] fs/fuse: " ira.weiny
2020-10-09 19:49 ` [PATCH RFC PKS/PMEM 24/58] fs/freevxfs: " ira.weiny
2020-10-13 11:25   ` Christoph Hellwig
2020-10-13 20:52     ` Ira Weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 25/58] fs/reiserfs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 26/58] fs/zonefs: " ira.weiny
2020-10-12  2:30   ` Damien Le Moal
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 27/58] fs/ubifs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 28/58] fs/cachefiles: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 29/58] fs/ntfs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 30/58] fs/romfs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 31/58] fs/vboxsf: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 32/58] fs/hostfs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 33/58] fs/cramfs: " ira.weiny
2020-10-13 18:36   ` Nicolas Pitre
2020-10-13 18:44   ` Dan Williams
2020-10-13 19:36     ` Matthew Wilcox
2020-10-13 19:41       ` Dan Williams
2020-10-13 20:01       ` Al Viro
2020-10-13 20:50         ` Ira Weiny
2020-10-13 20:45       ` Ira Weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 34/58] fs/erofs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 35/58] fs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 36/58] fs/ext2: Use ext2_put_page ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 37/58] fs/ext2: Utilize new kmap_thread() ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 38/58] fs/isofs: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 39/58] fs/jffs2: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 40/58] net: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 41/58] drivers/target: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 42/58] drivers/scsi: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 43/58] drivers/mmc: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 44/58] drivers/xen: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 45/58] drivers/firmware: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 46/58] drives/staging: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 47/58] drivers/mtd: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 48/58] drivers/md: " ira.weiny
2020-10-10  2:20   ` Coly Li
2020-10-12  5:28     ` Ira Weiny
2020-10-12  7:40       ` Coly Li
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 49/58] drivers/misc: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 50/58] drivers/android: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 51/58] kernel: " ira.weiny
2020-10-10  3:43   ` Eric W. Biederman
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 52/58] mm: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 53/58] lib: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 54/58] powerpc: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 55/58] samples: " ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 56/58] dax: Stray access protection for dax_direct_access() ira.weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 57/58] nvdimm/pmem: Stray access protection for pmem->virt_addr ira.weiny
2020-10-10  2:53   ` John Hubbard
2020-10-12  5:52     ` Ira Weiny
2020-10-09 19:50 ` [PATCH RFC PKS/PMEM 58/58] [dax|pmem]: Enable stray access protection ira.weiny
2020-10-10 11:36 ` [PATCH RFC PKS/PMEM 10/58] drivers/rdma: Utilize new kmap_thread() Bernard Metzler
2020-10-12  4:47   ` Ira Weiny

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