[Xen-devel] [PATCH 2/3] x86/paravirt: Add paravirt_{read, write}_msr

[Andy Lutomirski <luto@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 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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