Commit 6dd29b3d authored Apr 23, 2017 by Ingo Molnar

Revert "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation"



This reverts commit 2947ba05.

Dan Williams reported dax-pmem kernel warnings with the following signature:

   WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155 percpu_ref_switch_to_atomic_rcu+0x1f5/0x200
   percpu ref (dax_pmem_percpu_release [dax_pmem]) <= 0 (0) after switching to atomic

... and bisected it to this commit, which suggests possible memory corruption
caused by the x86 fast-GUP conversion.

He also pointed out:

 "
  This is similar to the backtrace when we were not properly handling
  pud faults and was fixed with this commit: 220ced16 "mm: fix
  get_user_pages() vs device-dax pud mappings"

  I've found some missing _devmap checks in the generic
  get_user_pages_fast() path, but this does not fix the regression
  [...]
 "

So given that there are known bugs, and a pretty robust looking bisection
points to this commit suggesting that are unknown bugs in the conversion
as well, revert it for the time being - we'll re-try in v4.13.

Reported-by: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: aneesh.kumar@linux.vnet.ibm.com
Cc: dann.frazier@canonical.com
Cc: dave.hansen@intel.com
Cc: steve.capper@linaro.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent ace2fb5a

arch/arm/Kconfig

+1 −1

Original line number	Diff line number	Diff line
		@@ -1666,7 +1666,7 @@ config ARCH_SELECT_MEMORY_MODEL
		config HAVE_ARCH_PFN_VALID
		def_bool ARCH_HAS_HOLES_MEMORYMODEL \|\| !SPARSEMEM

		config HAVE_GENERIC_GUP
		config HAVE_GENERIC_RCU_GUP
		def_bool y
		depends on ARM_LPAE

arch/arm64/Kconfig

+1 −1

Original line number	Diff line number	Diff line
		@@ -205,7 +205,7 @@ config GENERIC_CALIBRATE_DELAY
		config ZONE_DMA
		def_bool y

		config HAVE_GENERIC_GUP
		config HAVE_GENERIC_RCU_GUP
		def_bool y

		config ARCH_DMA_ADDR_T_64BIT

arch/powerpc/Kconfig

+1 −1

Original line number	Diff line number	Diff line
		@@ -135,7 +135,7 @@ config PPC
		select HAVE_FUNCTION_GRAPH_TRACER
		select HAVE_FUNCTION_TRACER
		select HAVE_GCC_PLUGINS
		select HAVE_GENERIC_GUP
		select HAVE_GENERIC_RCU_GUP
		select HAVE_HW_BREAKPOINT if PERF_EVENTS && (PPC_BOOK3S \|\| PPC_8xx)
		select HAVE_IDE
		select HAVE_IOREMAP_PROT

arch/x86/Kconfig

+0 −3

Original line number	Diff line number	Diff line
		@@ -2789,9 +2789,6 @@ config X86_DMA_REMAP
		bool
		depends on STA2X11

		config HAVE_GENERIC_GUP
		def_bool y

		source "net/Kconfig"

		source "drivers/Kconfig"

arch/x86/include/asm/mmu_context.h

+12 −0

Original line number	Diff line number	Diff line
		@@ -220,6 +220,18 @@ static inline int vma_pkey(struct vm_area_struct *vma)
		}
		#endif

		static inline bool __pkru_allows_pkey(u16 pkey, bool write)
		{
		u32 pkru = read_pkru();

		if (!__pkru_allows_read(pkru, pkey))
		return false;
		if (write && !__pkru_allows_write(pkru, pkey))
		return false;

		return true;
		}

		/*
		* We only want to enforce protection keys on the current process
		* because we effectively have no access to PKRU for other

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