[PATCH] x86/cpuid: Fix HLE and RTM handling (again)

[PATCH] x86/cpuid: Fix HLE and RTM handling (again)

[Andrew Cooper]

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,
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")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reported-by: Edwin Török <edvin.torok@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
---
 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 f3c8950aa3..958caf35da 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -672,9 +672,11 @@ 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);
 
-- 
2.11.0

Re: [PATCH] x86/cpuid: Fix HLE and RTM handling (again)

[Jan Beulich]

On 07.06.2021 14:41, Andrew Cooper wrote:
> 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,
> 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")
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Reported-by: Edwin Török <edvin.torok@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>