[PATCH v3 5/6] x86/alternative: Use a single access in text_poke() where possible

[Josh Poimboeuf]

Static call inline patching will need to use single 32-bit writes.
Change text_poke() to do so where possible.

Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
---
 arch/x86/kernel/alternative.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index ebeac487a20c..607f48a90097 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -692,7 +692,7 @@ void *__init_or_module text_poke_early(void *addr, const 
void *opcode,
 void *text_poke(void *addr, const void *opcode, size_t len)
 {
        unsigned long flags;
-       char *vaddr;
+       unsigned long vaddr;
        struct page *pages[2];
        int i;
 
@@ -714,14 +714,39 @@ void *text_poke(void *addr, const void *opcode, size_t 
len)
        }
        BUG_ON(!pages[0]);
        local_irq_save(flags);
+
        set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
        if (pages[1])
                set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
-       vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
-       memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
+
+       vaddr = fix_to_virt(FIX_TEXT_POKE0) + ((unsigned long)addr & 
~PAGE_MASK);
+
+       /*
+        * Use a single access where possible.  Note that a single unaligned
+        * multi-byte write will not necessarily be atomic on x86-32, or if the
+        * address crosses a cache line boundary.
+        */
+       switch (len) {
+       case 1:
+               WRITE_ONCE(*(u8 *)vaddr, *(u8 *)opcode);
+               break;
+       case 2:
+               WRITE_ONCE(*(u16 *)vaddr, *(u16 *)opcode);
+               break;
+       case 4:
+               WRITE_ONCE(*(u32 *)vaddr, *(u32 *)opcode);
+               break;
+       case 8:
+               WRITE_ONCE(*(u64 *)vaddr, *(u64 *)opcode);
+               break;
+       default:
+               memcpy((void *)vaddr, opcode, len);
+       }
+
        clear_fixmap(FIX_TEXT_POKE0);
        if (pages[1])
                clear_fixmap(FIX_TEXT_POKE1);
+
        local_flush_tlb();
        sync_core();
        /* Could also do a CLFLUSH here to speed up CPU recovery; but
-- 
2.17.2