From a1ac4cf52e38386bac7ac3440c7da0099662ca5c Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Tue, 29 Jul 2014 17:02:25 +0200 Subject: [PATCH] x86/cpu: undo BIOS CPUID max_leaf limit before querying for features If IA32_MISC_ENABLE[22] is set by the BIOS, CPUID.0.EAX will be limited to 3. Lift this limit before considering whether to query CPUID.7[ECX=0].EBX for features. Without this change, dom0 is able to see this feature leaf (as the limit was subsequently lifted), and will set features appropriately in HVM domain cpuid policies. The specific bug XenServer observed was the advertisement of the FSGSBASE feature, but an inability to set CR4.FSGSBASE as Xen considered the bit to be reserved as cpu_has_fsgsbase incorrectly evaluated as false. This is a regression introduced by c/s 44e24f8567 "x86: don't call generic_identify() redundantly" where the redundant call actually resampled CPUID.7[ECX=0] properly to obtain the feature flags. Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- xen/arch/x86/cpu/common.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c index 074169668b..5156df3105 100644 --- a/xen/arch/x86/cpu/common.c +++ b/xen/arch/x86/cpu/common.c @@ -250,14 +250,15 @@ static void __cpuinit generic_identify(struct cpuinfo_x86 *c) paddr_bits = cpuid_eax(0x80000008) & 0xff; } + /* Might lift BIOS max_leaf=3 limit. */ + early_intel_workaround(c); + /* Intel-defined flags: level 0x00000007 */ if ( c->cpuid_level >= 0x00000007 ) { u32 dummy; cpuid_count(0x00000007, 0, &dummy, &ebx, &dummy, &dummy); c->x86_capability[X86_FEATURE_FSGSBASE / 32] = ebx; } - - early_intel_workaround(c); } /* -- 2.30.2