linux-kernel - [PATCH 2/3] x86/paravirt: Add paravirt_{read,write}

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Message-Id: <54487a210e2b389c2504c6391d33053e8ea40963.1442445946.git.luto@kernel.org>
Date:	Wed, 16 Sep 2015 16:33:13 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	KVM list <kvm@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	xen-devel <Xen-devel@...ts.xen.org>,
	linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 2/3] x86/paravirt: Add paravirt_{read,write}_msr

This adds paravirt hooks for unsafe MSR access.  On native, they
call native_{read,write}_msr.  On Xen, they use
xen_{read,write}_msr_safe.

Nothing uses them yet for ease of bisection.  The next patch will
use them in rdmsrl, wrmsrl, etc.

I intentionally didn't make them OOPS on #GP on Xen.  I think that
should be done separately by the Xen maintainers.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/include/asm/paravirt.h       | 11 +++++++++++
 arch/x86/include/asm/paravirt_types.h | 10 ++++++++--
 arch/x86/kernel/paravirt.c            |  2 ++
 arch/x86/xen/enlighten.c              | 23 +++++++++++++++++++++++
 4 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 9cf6e5232b0d..e6569a3b0a37 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -123,6 +123,17 @@ static inline void wbinvd(void)
 
 #define get_kernel_rpl()  (pv_info.kernel_rpl)
 
+static inline u64 paravirt_read_msr(unsigned msr)
+{
+	return PVOP_CALL1(u64, pv_cpu_ops.read_msr, msr);
+}
+
+static inline void paravirt_write_msr(unsigned msr,
+				      unsigned low, unsigned high)
+{
+	return PVOP_VCALL3(pv_cpu_ops.write_msr, msr, low, high);
+}
+
 static inline u64 paravirt_read_msr_safe(unsigned msr, int *err)
 {
 	return PVOP_CALL2(u64, pv_cpu_ops.read_msr_safe, msr, err);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 810e8ccaa42a..cb1e7af9fe42 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -151,8 +151,14 @@ struct pv_cpu_ops {
 	void (*cpuid)(unsigned int *eax, unsigned int *ebx,
 		      unsigned int *ecx, unsigned int *edx);
 
-	/* MSR operations.
-	   err = 0/-EIO.  wrmsr returns 0/-EIO. */
+	/* Unsafe MSR operations.  These either succeed or crash. */
+	u64 (*read_msr)(unsigned int msr);
+	int (*write_msr)(unsigned int msr, unsigned low, unsigned high);
+
+	/*
+	 * Safe MSR operations.
+	 * err = 0/-EIO.  wrmsr returns 0/-EIO.
+	 */
 	u64 (*read_msr_safe)(unsigned int msr, int *err);
 	int (*write_msr_safe)(unsigned int msr, unsigned low, unsigned high);
 
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index fe8cd519a796..21fc4686f760 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -349,6 +349,8 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 	.write_cr8 = native_write_cr8,
 #endif
 	.wbinvd = native_wbinvd,
+	.read_msr = native_read_msr,
+	.write_msr = native_write_msr,
 	.read_msr_safe = native_read_msr_safe,
 	.write_msr_safe = native_write_msr_safe,
 	.read_pmc = native_read_pmc,
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 8523d42d163e..d2bc6afeaf33 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1086,6 +1086,26 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
 	return ret;
 }
 
+static u64 xen_read_msr(unsigned int msr)
+{
+	/*
+	 * This will silently swallow a #GP from RDMSR.  It may be worth
+	 * changing that.
+	 */
+	int err;
+
+	return xen_read_msr_safe(msr, &err);
+}
+
+static void xen_write_msr(unsigned int msr, unsigned low, unsigned high)
+{
+	/*
+	 * This will silently swallow a #GP from WRMSR.  It may be worth
+	 * changing that.
+	 */
+	xen_write_msr_safe(msr, low, high);
+}
+
 void xen_setup_shared_info(void)
 {
 	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
@@ -1216,6 +1236,9 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
 
 	.wbinvd = native_wbinvd,
 
+	.read_msr = xen_read_msr,
+	.write_msr = xen_write_msr,
+
 	.read_msr_safe = xen_read_msr_safe,
 	.write_msr_safe = xen_write_msr_safe,
 
-- 
2.4.3

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