[xen stable-4.16] x86/boot: Adjust MSR_ARCH_CAPS handling for the Host policy

[patchbot@xxxxxxx]

commit a21bfbd10b0daf46bd596b7bde2d0a6a9351ffa7
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon May 15 14:14:53 2023 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Aug 8 16:02:53 2023 +0100

    x86/boot: Adjust MSR_ARCH_CAPS handling for the Host policy
    
    We are about to move MSR_ARCH_CAPS into featureset, but the order of
    operations (copy raw policy, then copy x86_capabilitiles[] in) will end up
    clobbering the ARCH_CAPS value.
    
    Some toolstacks use this information to handle TSX compatibility across the
    CPUs and microcode versions where support was removed.
    
    To avoid this transient breakage, read from raw_cpu_policy rather than
    modifying it in place.  This logic will be removed entirely in due course.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 43912f8dbb1888ffd7f00adb10724c70e71927c4)
---
 xen/arch/x86/cpu-policy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
index 351973a866..b650af431c 100644
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -411,7 +411,7 @@ static void __init calculate_host_policy(void)
     p->platform_info.cpuid_faulting = cpu_has_cpuid_faulting;
 
     /* Temporary, until we have known_features[] for feature bits in MSRs. */
-    p->arch_caps.raw &=
+    p->arch_caps.raw = raw_cpu_policy.arch_caps.raw &
         (ARCH_CAPS_RDCL_NO | ARCH_CAPS_IBRS_ALL | ARCH_CAPS_RSBA |
          ARCH_CAPS_SKIP_L1DFL | ARCH_CAPS_SSB_NO | ARCH_CAPS_MDS_NO |
          ARCH_CAPS_IF_PSCHANGE_MC_NO | ARCH_CAPS_TSX_CTRL | ARCH_CAPS_TAA_NO |
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16