From e31c0d0d400f05b8e5eb20b3e5859d8319c1b4dc Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Tue, 25 May 2021 15:32:02 +0000 Subject: [PATCH] MIPS: Avoid DIVU in `__div64_32' is result would be zero stable inclusion from stable-5.10.38 commit d17af8b19d99c400a484427c88f973e6b1f842aa bugzilla: 51875 CVE: NA -------------------------------- commit c1d337d45ec0a802299688e17d568c4e3a585895 upstream. We already check the high part of the divident against zero to avoid the costly DIVU instruction in that case, needed to reduce the high part of the divident, so we may well check against the divisor instead and set the high part of the quotient to zero right away. We need to treat the high part the divident in that case though as the remainder that would be calculated by the DIVU instruction we avoided. This has passed correctness verification with test_div64 and reduced the module's average execution time down to 1.0445s and 0.2619s from 1.0668s and 0.2629s respectively for an R3400 CPU @40MHz and a 5Kc CPU @160MHz. Signed-off-by: Maciej W. Rozycki Signed-off-by: Thomas Bogendoerfer Signed-off-by: Greg Kroah-Hartman Signed-off-by: Chen Jun Acked-by: Weilong Chen Signed-off-by: Zheng Zengkai --- arch/mips/include/asm/div64.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/mips/include/asm/div64.h b/arch/mips/include/asm/div64.h index b252300e299d..a882a7bdf63e 100644 --- a/arch/mips/include/asm/div64.h +++ b/arch/mips/include/asm/div64.h @@ -68,9 +68,11 @@ \ __high = __div >> 32; \ __low = __div; \ - __upper = __high; \ \ - if (__high) { \ + if (__high < __radix) { \ + __upper = __high; \ + __high = 0; \ + } else { \ __asm__("divu $0, %z1, %z2" \ : "=x" (__modquot) \ : "Jr" (__high), "Jr" (__radix)); \ -- GitLab