From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 22 Sep 2014 11:17:48 +0000 (+0200)
Subject: x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only
X-Git-Tag: v3.2.66~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9a8d305befe3218c7523179c0d406d876b5cbbed;p=pandora-kernel.git

x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only

commit c1118b3602c2329671ad5ec8bdf8e374323d6343 upstream.

On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA.
In that case, KVM will fail to patch VMCALL instructions to VMMCALL
as required on AMD processors.

The failure mode is currently a divide-by-zero exception, which obviously
is a KVM bug that has to be fixed.  However, picking the right instruction
between VMCALL and VMMCALL will be faster and will help if you cannot upgrade
the hypervisor.

Reported-by: Chris Webb <chris@arachsys.com>
Tested-by: Chris Webb <chris@arachsys.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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