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Commit 6b0f43dd authored by Borislav Petkov's avatar Borislav Petkov Committed by H. Peter Anvin
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x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit 



fbd8b181 turns off the bit for
/proc/cpuinfo. However, a proper/full fix would be to additionally
turn off the bit in the CPUID output so that future callers get
correct CPU features info.

Do that by basically reversing what the BIOS wrongfully does at boot.

Signed-off-by: default avatarBorislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <1251705011-18636-3-git-send-email-petkovbb@gmail.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 177fed1e

arch/x86/kernel/cpu/amd.c

+10 −1
Original line number Diff line number Diff line
@@ -404,9 +404,18 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c) 
		/*

		 * Some BIOSes incorrectly force this feature, but only K8

		 * revision D (model = 0x14) and later actually support it.

		 * (AMD Erratum #110, docId: 25759).

		 */

		if (c->x86_model < 0x14)

		if (c->x86_model < 0x14 && cpu_has(c, X86_FEATURE_LAHF_LM)) {

			u64 val;



			clear_cpu_cap(c, X86_FEATURE_LAHF_LM);

			if (!rdmsrl_amd_safe(0xc001100d, &val)) {

				val &= ~(1ULL << 32);

				wrmsrl_amd_safe(0xc001100d, val);

			}

		}



	}

	if (c->x86 == 0x10 || c->x86 == 0x11)

		set_cpu_cap(c, X86_FEATURE_REP_GOOD);