0018-x86-CPUID-surface-suitable-value-in-EBX-of-XSTATE-su.patch


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From e8882bcfe35520e950ba60acd6e67e65f1ce90a8 Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Tue, 11 Oct 2022 14:59:26 +0200
Subject: [PATCH 18/87] x86/CPUID: surface suitable value in EBX of XSTATE
 subleaf 1

While the SDM isn't very clear about this, our present behavior make
Linux 5.19 unhappy. As of commit 8ad7e8f69695 ("x86/fpu/xsave: Support
XSAVEC in the kernel") they're using this CPUID output also to size
the compacted area used by XSAVEC. Getting back zero there isn't really
liked, yet for PV that's the default on capable hardware: XSAVES isn't
exposed to PV domains.

Considering that the size reported is that of the compacted save area,
I view Linux'es assumption as appropriate (short of the SDM properly
considering the case). Therefore we need to populate the field also when
only XSAVEC is supported for a guest.

Fixes: 460b9a4b3630 ("x86/xsaves: enable xsaves/xrstors for hvm guest")
Fixes: 8d050ed1097c ("x86: don't expose XSAVES capability to PV guests")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: c3bd0b83ea5b7c0da6542687436042eeea1e7909
master date: 2022-08-24 14:23:59 +0200
---
 xen/arch/x86/cpuid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index ff335f16390d..a647331f4793 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -1060,7 +1060,7 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf,
         switch ( subleaf )
         {
         case 1:
-            if ( p->xstate.xsaves )
+            if ( p->xstate.xsavec || p->xstate.xsaves )
             {
                 /*
                  * TODO: Figure out what to do for XSS state.  VT-x manages
-- 
2.37.4