[Xen-changelog] [xen stable-4.2] x86/cpu: undo BIOS CPUID max_leaf limit before querying for features

[patchbot@xxxxxxx]

commit 35e7ae5f66f34bd93dff089587da3b3665622eff
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Aug 12 16:10:01 2014 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Aug 12 16:10:01 2014 +0200

    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 <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: a1ac4cf52e38386bac7ac3440c7da0099662ca5c
    master date: 2014-07-29 17:02:25 +0200
---
 xen/arch/x86/cpu/common.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 44542f4..22fa2a6 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -271,6 +271,9 @@ 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;
@@ -278,8 +281,6 @@ static void __cpuinit generic_identify(struct cpuinfo_x86 
*c)
                c->x86_capability[X86_FEATURE_FSGSBASE / 32] = ebx;
        }
 
-       early_intel_workaround(c);
-
 #ifdef CONFIG_X86_HT
        c->phys_proc_id = (cpuid_ebx(1) >> 24) & 0xff;
 #endif
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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