[linux-next RFC] mm/gup.c: Convert to use get_user_pages_fast_only()

[Souptick Joarder <jrdr.linux@gmail.com>]

Renaming the API __get_user_pages_fast() to get_user_pages_
fast_only() to align with pin_user_pages_fast_only().

As part of this we will get rid of write parameter.
Instead caller will pass FOLL_WRITE to get_user_pages_fast_only().
This will not change any existing functionality of the API.

All the callers are changed to pass FOLL_WRITE.

Updated the documentation of the API.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
---
 arch/powerpc/kvm/book3s_64_mmu_hv.c    |  2 +-
 arch/powerpc/kvm/book3s_64_mmu_radix.c |  2 +-
 arch/powerpc/perf/callchain_64.c       |  2 +-
 include/linux/mm.h                     |  4 ++--
 kernel/events/core.c                   |  4 ++--
 mm/gup.c                               | 29 ++++++++++++++++-------------
 virt/kvm/kvm_main.c                    |  6 +++---
 7 files changed, 26 insertions(+), 23 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 18aed97..34fc5c8 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -581,7 +581,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	 * We always ask for write permission since the common case
 	 * is that the page is writable.
 	 */
-	if (__get_user_pages_fast(hva, 1, 1, &page) == 1) {
+	if (get_user_pages_fast_only(hva, 1, FOLL_WRITE, &page) == 1) {
 		write_ok = true;
 	} else {
 		/* Call KVM generic code to do the slow-path check */
diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 3248f78..3b6e342 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -795,7 +795,7 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
 	 * is that the page is writable.
 	 */
 	hva = gfn_to_hva_memslot(memslot, gfn);
-	if (!kvm_ro && __get_user_pages_fast(hva, 1, 1, &page) == 1) {
+	if (!kvm_ro && get_user_pages_fast_only(hva, 1, FOLL_WRITE, &page) == 1) {
 		upgrade_write = true;
 	} else {
 		unsigned long pfn;
diff --git a/arch/powerpc/perf/callchain_64.c b/arch/powerpc/perf/callchain_64.c
index 1bff896d..f719a74 100644
--- a/arch/powerpc/perf/callchain_64.c
+++ b/arch/powerpc/perf/callchain_64.c
@@ -32,7 +32,7 @@ int read_user_stack_slow(void __user *ptr, void *buf, int nb)
 	int nrpages;
 	void *kaddr;
 
-	nrpages = __get_user_pages_fast(addr, 1, 1, &page);
+	nrpages = get_user_pages_fast_only(addr, 1, FOLL_WRITE, &page);
 	if (nrpages == 1) {
 		kaddr = page_address(page);
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 93d93bd..10a6758 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1817,8 +1817,8 @@ extern int mprotect_fixup(struct vm_area_struct *vma,
 /*
  * doesn't attempt to fault and will return short.
  */
-int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
-			  struct page **pages);
+int get_user_pages_fast_only(unsigned long start, int nr_pages,
+			unsigned int gup_flags, struct page **pages);
 int pin_user_pages_fast_only(unsigned long start, int nr_pages,
 			     unsigned int gup_flags, struct page **pages);
 /*
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c94eb27..81d6e73 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6934,12 +6934,12 @@ static u64 perf_virt_to_phys(u64 virt)
 		 * Walking the pages tables for user address.
 		 * Interrupts are disabled, so it prevents any tear down
 		 * of the page tables.
-		 * Try IRQ-safe __get_user_pages_fast first.
+		 * Try IRQ-safe get_user_pages_fast_only first.
 		 * If failed, leave phys_addr as 0.
 		 */
 		if (current->mm != NULL) {
 			pagefault_disable();
-			if (__get_user_pages_fast(virt, 1, 0, &p) == 1)
+			if (get_user_pages_fast_only(virt, 1, 0, &p) == 1)
 				phys_addr = page_to_phys(p) + virt % PAGE_SIZE;
 			pagefault_enable();
 		}
diff --git a/mm/gup.c b/mm/gup.c
index 80f51a36..d8aabc0 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2278,7 +2278,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
  * to be special.
  *
  * For a futex to be placed on a THP tail page, get_futex_key requires a
- * __get_user_pages_fast implementation that can pin pages. Thus it's still
+ * get_user_pages_fast_only implementation that can pin pages. Thus it's still
  * useful to have gup_huge_pmd even if we can't operate on ptes.
  */
 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
@@ -2683,7 +2683,7 @@ static inline void gup_pgd_range(unsigned long addr, unsigned long end,
 
 #ifndef gup_fast_permitted
 /*
- * Check if it's allowed to use __get_user_pages_fast() for the range, or
+ * Check if it's allowed to use get_user_pages_fast_only() for the range, or
  * we need to fall back to the slow version:
  */
 static bool gup_fast_permitted(unsigned long start, unsigned long end)
@@ -2776,8 +2776,14 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
 
 	return ret;
 }
-
-/*
+/**
+ * get_user_pages_fast_only() - pin user pages in memory
+ * @start:      starting user address
+ * @nr_pages:   number of pages from start to pin
+ * @gup_flags:  flags modifying pin behaviour
+ * @pages:      array that receives pointers to the pages pinned.
+ *              Should be at least nr_pages long.
+ *
  * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
  * the regular GUP.
  * Note a difference with get_user_pages_fast: this always returns the
@@ -2786,8 +2792,8 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
  * If the architecture does not support this function, simply return with no
  * pages pinned.
  */
-int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
-			  struct page **pages)
+int get_user_pages_fast_only(unsigned long start, int nr_pages,
+			unsigned int gup_flags, struct page **pages)
 {
 	int nr_pinned;
 	/*
@@ -2797,10 +2803,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	 * FOLL_FAST_ONLY is required in order to match the API description of
 	 * this routine: no fall back to regular ("slow") GUP.
 	 */
-	unsigned int gup_flags = FOLL_GET | FOLL_FAST_ONLY;
-
-	if (write)
-		gup_flags |= FOLL_WRITE;
+	gup_flags = FOLL_GET | FOLL_FAST_ONLY;
 
 	nr_pinned = internal_get_user_pages_fast(start, nr_pages, gup_flags,
 						 pages);
@@ -2815,7 +2818,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 
 	return nr_pinned;
 }
-EXPORT_SYMBOL_GPL(__get_user_pages_fast);
+EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
 
 /**
  * get_user_pages_fast() - pin user pages in memory
@@ -2886,8 +2889,8 @@ int pin_user_pages_fast(unsigned long start, int nr_pages,
 EXPORT_SYMBOL_GPL(pin_user_pages_fast);
 
 /*
- * This is the FOLL_PIN equivalent of __get_user_pages_fast(). Behavior is the
- * same, except that this one sets FOLL_PIN instead of FOLL_GET.
+ * This is the FOLL_PIN equivalent of get_user_pages_fast_only(). Behavior
+ * is the same, except that this one sets FOLL_PIN instead of FOLL_GET.
  *
  * The API rules are the same, too: no negative values may be returned.
  */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fc38d63..cec7919 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1750,7 +1750,7 @@ static bool hva_to_pfn_fast(unsigned long addr, bool write_fault,
 	if (!(write_fault || writable))
 		return false;
 
-	npages = __get_user_pages_fast(addr, 1, 1, page);
+	npages = get_user_pages_fast_only(addr, 1, FOLL_WRITE, page);
 	if (npages == 1) {
 		*pfn = page_to_pfn(page[0]);
 
@@ -1791,7 +1791,7 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
 	if (unlikely(!write_fault) && writable) {
 		struct page *wpage;
 
-		if (__get_user_pages_fast(addr, 1, 1, &wpage) == 1) {
+		if (get_user_pages_fast_only(addr, 1, FOLL_WRITE, &wpage) == 1) {
 			*writable = true;
 			put_page(page);
 			page = wpage;
@@ -1998,7 +1998,7 @@ int gfn_to_page_many_atomic(struct kvm_memory_slot *slot, gfn_t gfn,
 	if (entry < nr_pages)
 		return 0;
 
-	return __get_user_pages_fast(addr, nr_pages, 1, pages);
+	return get_user_pages_fast(addr, nr_pages, FOLL_WRITE, pages);
 }
 EXPORT_SYMBOL_GPL(gfn_to_page_many_atomic);
 
-- 
1.9.1