From a8c171c107c0b61a5e7e10cedab0fb72aeaf640d Mon Sep 17 00:00:00 2001 From: Mauricio Faria de Oliveira Date: Thu, 23 Jul 2026 20:08:04 -0300 Subject: [PATCH 1/2] x86/boot: Add volatile, clobbers and zero-length test in memcmp() Add the volatile qualifier and clobbers parameter to prevent bugs with instruction reordering and optimization. Also add TEST for the zero-length case to set ZF, as, if the count register is zero, the REPE prefix does not run the CMPSB instruction, leaving the ZF flag undetermined. [ bp: Add a comment about the len==0 case. ] Fixes: 62bd0337d0c4 ("Top header file for new x86 setup code") Closes: https://sashiko.dev/#/patchset/20260701-pvh-kasan-inline-v6-0-ba99045dfa9f%40igalia.com Suggested-by: Borislav Petkov Signed-off-by: Mauricio Faria de Oliveira Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/all/20260721-pvh-kasan-inline-v7-2-38979a50cef0@igalia.com --- arch/x86/boot/string.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c index ac0f900ebc47..1632d40e1f54 100644 --- a/arch/x86/boot/string.c +++ b/arch/x86/boot/string.c @@ -32,8 +32,15 @@ int memcmp(const void *s1, const void *s2, size_t len) { bool diff; - asm("repe cmpsb" - : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len)); + + /* + * Make sure ZF is properly set in the len==0 case because in it, + * RCX==0 and the REPE; CMPSB won't get executed. + */ + asm volatile("test %3, %3\n\t" + "repe cmpsb" + : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len) + : : "cc", "memory"); return diff; } From 52075128273ace53e6254e37899a47d40d4baf45 Mon Sep 17 00:00:00 2001 From: Pratik Vishwakarma Date: Wed, 29 Jul 2026 05:54:59 +0000 Subject: [PATCH 2/2] x86/CPU/AMD: Carve out a Zen5 models range Family 0x1a, model 0xd0..0xd7 belongs to the Zen5 generation. Carve it out from the larger, Zen6 range where former doesn't belong. [ bp: Rewrite commit message, add tags. ] Fixes: b5f53e6d3d32 ("x86/CPU/AMD: Add more Zen6 models") Signed-off-by: Pratik Vishwakarma Signed-off-by: Borislav Petkov (AMD) Cc: Link: https://patch.msgid.link/20260729055459.15904-1-Pratik.Vishwakarma@amd.com --- arch/x86/kernel/cpu/amd.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 487ac147e11f..d61df70d6875 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -515,11 +515,13 @@ static void bsp_init_amd(struct cpuinfo_x86 *c) case 0x00 ... 0x2f: case 0x40 ... 0x4f: case 0x60 ... 0x7f: + case 0xd0 ... 0xd7: setup_force_cpu_cap(X86_FEATURE_ZEN5); break; case 0x50 ... 0x5f: case 0x80 ... 0xaf: - case 0xc0 ... 0xef: + case 0xc0 ... 0xcf: + case 0xd8 ... 0xef: setup_force_cpu_cap(X86_FEATURE_ZEN6); break; default: