[xen stable-4.15] x86/AMD: extend Zenbleed check to models "good" ucode isn't known for

[patchbot@xxxxxxx]

commit db3386e6cad6065c2a9155d4056b59164edb64dd
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Aug 23 09:26:36 2023 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Sep 19 19:38:35 2023 +0100

    x86/AMD: extend Zenbleed check to models "good" ucode isn't known for
    
    Reportedly the AMD Custom APU 0405 found on SteamDeck, models 0x90 and
    0x91, (quoting the respective Linux commit) is similarly affected. Put
    another instance of our Zen1 vs Zen2 distinction checks in
    amd_check_zenbleed(), forcing use of the chickenbit irrespective of
    ucode version (building upon real hardware never surfacing a version of
    0xffffffff).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    (cherry picked from commit 145a69c0944ac70cfcf9d247c85dee9e99d9d302)
---
 xen/arch/x86/cpu/amd.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 82375bf242..d8b78ae111 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -783,10 +783,17 @@ void amd_check_zenbleed(void)
        case 0xa0 ... 0xaf: good_rev = 0x08a00008; break;
        default:
                /*
-                * With the Fam17h check above, parts getting here are Zen1.
-                * They're not affected.
+                * With the Fam17h check above, most parts getting here are
+                * Zen1.  They're not affected.  Assume Zen2 ones making it
+                * here are affected regardless of microcode version.
+                *
+                * Zen1 vs Zen2 isn't a simple model number comparison, so use
+                * STIBP as a heuristic to distinguish.
                 */
-               return;
+               if (!boot_cpu_has(X86_FEATURE_AMD_STIBP))
+                       return;
+               good_rev = ~0U;
+               break;
        }
 
        rdmsrl(MSR_AMD64_DE_CFG, val);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.15