4.20-stable review patch. If anyone has any objections, please let me know.
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From: Eugeniy Paltsev Eugeniy.Paltsev@synopsys.com
commit e6a72b7daeeb521753803550f0ed711152bb2555 upstream.
ARCv2 optimized memset uses PREFETCHW instruction for prefetching the next cache line but doesn't ensure that the line is not past the end of the buffer. PRETECHW changes the line ownership and marks it dirty, which can cause issues in SMP config when next line was already owned by other core. Fix the issue by avoiding the PREFETCHW
Some more details:
The current code has 3 logical loops (ignroing the unaligned part) (a) Big loop for doing aligned 64 bytes per iteration with PREALLOC (b) Loop for 32 x 2 bytes with PREFETCHW (c) any left over bytes
loop (a) was already eliding the last 64 bytes, so PREALLOC was safe. The fix was removing PREFETCW from (b).
Another potential issue (applicable to configs with 32 or 128 byte L1 cache line) is that PREALLOC assumes 64 byte cache line and may not do the right thing specially for 32b. While it would be easy to adapt, there are no known configs with those lie sizes, so for now, just compile out PREALLOC in such cases.
Signed-off-by: Eugeniy Paltsev Eugeniy.Paltsev@synopsys.com Cc: stable@vger.kernel.org #4.4+ Signed-off-by: Vineet Gupta vgupta@synopsys.com [vgupta: rewrote changelog, used asm .macro vs. "C" macro] Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arc/lib/memset-archs.S | 40 ++++++++++++++++++++++++++++++++-------- 1 file changed, 32 insertions(+), 8 deletions(-)
--- a/arch/arc/lib/memset-archs.S +++ b/arch/arc/lib/memset-archs.S @@ -7,11 +7,39 @@ */
#include <linux/linkage.h> +#include <asm/cache.h>
-#undef PREALLOC_NOT_AVAIL +/* + * The memset implementation below is optimized to use prefetchw and prealloc + * instruction in case of CPU with 64B L1 data cache line (L1_CACHE_SHIFT == 6) + * If you want to implement optimized memset for other possible L1 data cache + * line lengths (32B and 128B) you should rewrite code carefully checking + * we don't call any prefetchw/prealloc instruction for L1 cache lines which + * don't belongs to memset area. + */ + +#if L1_CACHE_SHIFT == 6 + +.macro PREALLOC_INSTR reg, off + prealloc [\reg, \off] +.endm + +.macro PREFETCHW_INSTR reg, off + prefetchw [\reg, \off] +.endm + +#else + +.macro PREALLOC_INSTR +.endm + +.macro PREFETCHW_INSTR +.endm + +#endif
ENTRY_CFI(memset) - prefetchw [r0] ; Prefetch the write location + PREFETCHW_INSTR r0, 0 ; Prefetch the first write location mov.f 0, r2 ;;; if size is zero jz.d [blink] @@ -48,11 +76,8 @@ ENTRY_CFI(memset)
lpnz @.Lset64bytes ;; LOOP START -#ifdef PREALLOC_NOT_AVAIL - prefetchw [r3, 64] ;Prefetch the next write location -#else - prealloc [r3, 64] -#endif + PREALLOC_INSTR r3, 64 ; alloc next line w/o fetching + #ifdef CONFIG_ARC_HAS_LL64 std.ab r4, [r3, 8] std.ab r4, [r3, 8] @@ -85,7 +110,6 @@ ENTRY_CFI(memset) lsr.f lp_count, r2, 5 ;Last remaining max 124 bytes lpnz .Lset32bytes ;; LOOP START - prefetchw [r3, 32] ;Prefetch the next write location #ifdef CONFIG_ARC_HAS_LL64 std.ab r4, [r3, 8] std.ab r4, [r3, 8]