x86/paravirt: Add paravirt_{read,write}_msr()

This adds paravirt callbacks 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 warn on #GP on Xen.  I think that
should be done separately by the Xen maintainers.

Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: KVM list <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel <Xen-devel@lists.xen.org>
Link: http://lkml.kernel.org/r/880eebc5dcd2ad9f310d41345f82061ea500e9fa.1459605520.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 13f756fdcb33..6ab672233ac9 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1092,6 +1092,26 @@ 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)) {
@@ -1222,6 +1242,9 @@ 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,