x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementa…

…tion

This patch provides all required callbacks required by the generic
get_user_pages_fast() code and switches x86 over - and removes
the platform specific implementation.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20170606113133.22974-2-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/arm/Kconfig

@@ -1637,7 +1637,7 @@ config ARCH_SELECT_MEMORY_MODEL
 config HAVE_ARCH_PFN_VALID
 	def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM
 
-config HAVE_GENERIC_RCU_GUP
+config HAVE_GENERIC_GUP
 	def_bool y
 	depends on ARM_LPAE
 

arch/arm64/Kconfig

@@ -205,7 +205,7 @@ config GENERIC_CALIBRATE_DELAY
 config ZONE_DMA
 	def_bool y
 
-config HAVE_GENERIC_RCU_GUP
+config HAVE_GENERIC_GUP
 	def_bool y
 
 config ARCH_DMA_ADDR_T_64BIT

arch/powerpc/Kconfig

@@ -184,7 +184,7 @@ config PPC
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER
 	select HAVE_GCC_PLUGINS
-	select HAVE_GENERIC_RCU_GUP
+	select HAVE_GENERIC_GUP
 	select HAVE_HW_BREAKPOINT		if PERF_EVENTS && (PPC_BOOK3S || PPC_8xx)
 	select HAVE_IDE
 	select HAVE_IOREMAP_PROT

arch/x86/Kconfig

@@ -2797,6 +2797,9 @@ 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

@@ -218,18 +218,6 @@ 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

arch/x86/include/asm/pgtable-3level.h

@@ -212,4 +212,51 @@ static inline pud_t native_pudp_get_and_clear(pud_t *pudp)
 #define __pte_to_swp_entry(pte)		((swp_entry_t){ (pte).pte_high })
 #define __swp_entry_to_pte(x)		((pte_t){ { .pte_high = (x).val } })
 
+#define gup_get_pte gup_get_pte
+/*
+ * WARNING: only to be used in the get_user_pages_fast() implementation.
+ *
+ * With get_user_pages_fast(), we walk down the pagetables without taking
+ * any locks.  For this we would like to load the pointers atomically,
+ * but that is not possible (without expensive cmpxchg8b) on PAE.  What
+ * we do have is the guarantee that a PTE will only either go from not
+ * present to present, or present to not present or both -- it will not
+ * switch to a completely different present page without a TLB flush in
+ * between; something that we are blocking by holding interrupts off.
+ *
+ * Setting ptes from not present to present goes:
+ *
+ *   ptep->pte_high = h;
+ *   smp_wmb();
+ *   ptep->pte_low = l;
+ *
+ * And present to not present goes:
+ *
+ *   ptep->pte_low = 0;
+ *   smp_wmb();
+ *   ptep->pte_high = 0;
+ *
+ * We must ensure here that the load of pte_low sees 'l' iff pte_high
+ * sees 'h'. We load pte_high *after* loading pte_low, which ensures we
+ * don't see an older value of pte_high.  *Then* we recheck pte_low,
+ * which ensures that we haven't picked up a changed pte high. We might
+ * have gotten rubbish values from pte_low and pte_high, but we are
+ * guaranteed that pte_low will not have the present bit set *unless*
+ * it is 'l'. Because get_user_pages_fast() only operates on present ptes
+ * we're safe.
+ */
+static inline pte_t gup_get_pte(pte_t *ptep)
+{
+	pte_t pte;
+
+	do {
+		pte.pte_low = ptep->pte_low;
+		smp_rmb();
+		pte.pte_high = ptep->pte_high;
+		smp_rmb();
+	} while (unlikely(pte.pte_low != ptep->pte_low));
+
+	return pte;
+}
+
 #endif /* _ASM_X86_PGTABLE_3LEVEL_H */

arch/x86/include/asm/pgtable.h

@@ -244,6 +244,11 @@ static inline int pud_devmap(pud_t pud)
 	return 0;
 }
 #endif
+
+static inline int pgd_devmap(pgd_t pgd)
+{
+	return 0;
+}
 #endif
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
@@ -1185,6 +1190,54 @@ static inline u16 pte_flags_pkey(unsigned long pte_flags)
 #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;
+}
+
+/*
+ * 'pteval' can come from a PTE, PMD or PUD.  We only check
+ * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which are the
+ * same value on all 3 types.
+ */
+static inline bool __pte_access_permitted(unsigned long pteval, bool write)
+{
+	unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
+
+	if (write)
+		need_pte_bits |= _PAGE_RW;
+
+	if ((pteval & need_pte_bits) != need_pte_bits)
+		return 0;
+
+	return __pkru_allows_pkey(pte_flags_pkey(pteval), write);
+}
+
+#define pte_access_permitted pte_access_permitted
+static inline bool pte_access_permitted(pte_t pte, bool write)
+{
+	return __pte_access_permitted(pte_val(pte), write);
+}
+
+#define pmd_access_permitted pmd_access_permitted
+static inline bool pmd_access_permitted(pmd_t pmd, bool write)
+{
+	return __pte_access_permitted(pmd_val(pmd), write);
+}
+
+#define pud_access_permitted pud_access_permitted
+static inline bool pud_access_permitted(pud_t pud, bool write)
+{
+	return __pte_access_permitted(pud_val(pud), write);
+}
+
 #include <asm-generic/pgtable.h>
 #endif	/* __ASSEMBLY__ */
 

arch/x86/include/asm/pgtable_64.h

@@ -227,6 +227,20 @@ extern void cleanup_highmap(void);
 extern void init_extra_mapping_uc(unsigned long phys, unsigned long size);
 extern void init_extra_mapping_wb(unsigned long phys, unsigned long size);
 
-#endif /* !__ASSEMBLY__ */
+#define gup_fast_permitted gup_fast_permitted
+static inline bool gup_fast_permitted(unsigned long start, int nr_pages,
+		int write)
+{
+	unsigned long len, end;
+
+	len = (unsigned long)nr_pages << PAGE_SHIFT;
+	end = start + len;
+	if (end < start)
+		return false;
+	if (end >> __VIRTUAL_MASK_SHIFT)
+		return false;
+	return true;
+}
 
+#endif /* !__ASSEMBLY__ */
 #endif /* _ASM_X86_PGTABLE_64_H */

arch/x86/mm/Makefile

@@ -2,7 +2,7 @@
 KCOV_INSTRUMENT_tlb.o	:= n
 
 obj-y	:=  init.o init_$(BITS).o fault.o ioremap.o extable.o pageattr.o mmap.o \
-	    pat.o pgtable.o physaddr.o gup.o setup_nx.o tlb.o
+	    pat.o pgtable.o physaddr.o setup_nx.o tlb.o
 
 # Make sure __phys_addr has no stackprotector
 nostackp := $(call cc-option, -fno-stack-protector)