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From: Roger Pau Monne <roger.pau@citrix.com>
To: <xen-devel@lists.xenproject.org>
Cc: Roger Pau Monne <roger.pau@citrix.com>,
	Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: [PATCH] x86/cpuid: do not expand max leaves on restore
Date: Fri, 23 Apr 2021 12:54:08 +0200	[thread overview]
Message-ID: <20210423105408.7265-1-roger.pau@citrix.com> (raw)

When restoring limit the maximum leaves to the ones supported by Xen
4.13 in order to not expand the maximum leaf a guests sees. Note this
is unlikely to cause real issues.

Guests restored from Xen versions 4.13 or greater will contain CPUID
data on the stream that will override the values set by

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
 tools/libs/guest/xg_cpuid_x86.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
index 5ea69ad3d51..9296fdc34bd 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -510,6 +510,11 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid, bool restore,
             p->feat.mpx = test_bit(X86_FEATURE_MPX, host_featureset);
+        /* Clamp maximum leaves to the supported ones on 4.13. */
+        p->basic.max_leaf = min(p->basic.max_leaf, 0xdu);
+        p->feat.max_subleaf = min(p->feat.max_subleaf, 1u);
+        p->extd.max_leaf = min(p->extd.max_leaf, 0x1cu);
     if ( featureset )

             reply	other threads:[~2021-04-23 10:54 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-23 10:54 Roger Pau Monne [this message]
2021-04-23 12:41 ` [PATCH] x86/cpuid: do not expand max leaves on restore Jan Beulich
2021-04-23 12:47   ` Roger Pau Monné

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