linux-kernel - [PATCH] xen/x86: Don't try to write syscall-related MSRs for PV guests

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Date:	Mon, 21 Sep 2015 09:09:28 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	konrad.wilk@...cle.com, david.vrabel@...rix.com
Cc:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	boris.ostrovsky@...cle.com
Subject: [PATCH] xen/x86: Don't try to write syscall-related MSRs for PV guests

For PV guests these registers are set up by hypervisor and thus
should not be written by the guest. The comment in xen_write_msr_safe()
says so but we still write the MSRs, causing the hypervisor to
print a warning.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
---
 arch/x86/xen/enlighten.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 30d12af..1f1dbd2 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1077,6 +1077,7 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
 		/* Fast syscall setup is all done in hypercalls, so
 		   these are all ignored.  Stub them out here to stop
 		   Xen console noise. */
+		break;
 
 	default:
 		if (!pmu_msr_write(msr, low, high, &ret))
-- 
2.1.0

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