[xen stable-4.15] x86/cpuid: Fix HLE and RTM handling (again)

[patchbot@xxxxxxx]

commit 4586e6443a8b963283bdec1d72d42fae061ebc49
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jun 7 13:25:09 2021 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Jun 17 14:36:15 2021 +0100

    x86/cpuid: Fix HLE and RTM handling (again)
    
    For reasons which are my fault, but I don't recall why, the
    FDP_EXCP_ONLY/NO_FPU_SEL adjustment uses the whole special_features[] array
    element, not the two relevant bits.
    
    HLE and RTM were recently added to the list of special features, causing 
them
    to be always set in guest view, irrespective of the toolstacks choice on the
    matter.
    
    Rewrite the logic to refer to the features specifically, rather than relying
    on the contents of the special_features[] array.
    
    Fixes: 8fe24090d9 ("x86/cpuid: Rework HLE and RTM handling")
    Reported-by: Edwin Török <edvin.torok@xxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 60fa12dbf1d4d2c4ffe1ef34b495b24aa7e41aa0)
---
 xen/arch/x86/cpuid.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index 431f6fb173..eefcde902e 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -640,9 +640,11 @@ void recalculate_cpuid_policy(struct domain *d)
     sanitise_featureset(fs);
 
     /* Fold host's FDP_EXCP_ONLY and NO_FPU_SEL into guest's view. */
-    fs[FEATURESET_7b0] &= ~special_features[FEATURESET_7b0];
+    fs[FEATURESET_7b0] &= ~(cpufeat_mask(X86_FEATURE_FDP_EXCP_ONLY) |
+                            cpufeat_mask(X86_FEATURE_NO_FPU_SEL));
     fs[FEATURESET_7b0] |= (host_cpuid_policy.feat._7b0 &
-                           special_features[FEATURESET_7b0]);
+                           (cpufeat_mask(X86_FEATURE_FDP_EXCP_ONLY) |
+                            cpufeat_mask(X86_FEATURE_NO_FPU_SEL)));
 
     cpuid_featureset_to_policy(fs, p);
 
--
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