[PATCH v2] x86/msr: don't inject #GP when trying to read FEATURE_CONTROL

From: Roger Pau Monne <roger.pau@citrix.com>
To: <xen-devel@lists.xenproject.org>
Cc: Roger Pau Monne <roger.pau@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>
Subject: [PATCH v2] x86/msr: don't inject #GP when trying to read FEATURE_CONTROL
Date: Tue, 29 Dec 2020 17:58:01 +0100	[thread overview]
Message-ID: <20201229165801.89974-1-roger.pau@citrix.com> (raw)

Windows 10 will triple fault if #GP is injected when attempting to
read the FEATURE_CONTROL MSR on Intel or compatible hardware. Fix this
by injecting a #GP only when the vendor doesn't support the MSR, even
if there are no features to expose.

Fixes: 39ab598c50a2 ('x86/pv: allow reading FEATURE_CONTROL MSR')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
Changes since v1:
 - Allow Shanghai CPUs to access FEATURE_CONTROL without #GP.
---
 xen/arch/x86/msr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index be8e363862..6dfd3d5f97 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -176,7 +176,8 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
     switch ( msr )
     {
     case MSR_IA32_FEATURE_CONTROL:
-        if ( !cp->basic.vmx && !vmce_has_lmce(v) )
+        if ( !(cp->x86_vendor & (X86_VENDOR_INTEL | X86_VENDOR_CENTAUR |
+                                 X86_VENDOR_SHANGHAI)) )
             goto gp_fault;
 
         *val = IA32_FEATURE_CONTROL_LOCK;
-- 
2.29.2


