[xen stable-4.20] x86/pv: fix emulation of wb{,no}invd to flush all pCPU caches

[patchbot@xxxxxxx]

commit a60e95308072355dbe966c2129c0315f8222da30
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Jun 26 08:34:24 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jun 26 08:34:24 2025 +0200

    x86/pv: fix emulation of wb{,no}invd to flush all pCPU caches
    
    The current emulation of wb{,no}invd is bogus for PV guests: it will only
    flush the current pCPU cache, without taking into account pCPUs where the
    vCPU had run previously.  Resort to flushing the cache on all host pCPUs to
    make it correct.
    
    Fixes: 799fed0a7cc5 ("Priv-op emulation in Xen, for RDMSR/WRMSR/WBINVD")
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    [backport: no FLUSH_CACHE_WRITEBACK]
    master commit: b0f8bf86057b8f01fb4e48b506805d3818600f76
    master date: 2025-05-20 16:35:52 +0200
---
 xen/arch/x86/pv/emul-priv-op.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 295d847ea2..a21d499519 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -1198,13 +1198,11 @@ static int cf_check cache_op(
     if ( !cache_flush_permitted(current->domain) )
         /*
          * Non-physdev domain attempted WBINVD; ignore for now since
-         * newer linux uses this in some start-of-day timing loops.
+         * Linux uses this in some start-of-day code.
          */
         ;
-    else if ( op == x86emul_wbnoinvd /* && cpu_has_wbnoinvd */ )
-        wbnoinvd();
     else
-        wbinvd();
+        flush_all(FLUSH_CACHE);
 
     return X86EMUL_OKAY;
 }
--
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