x86/fsgsbase: Fix Xen PV support

On Xen PV, SWAPGS doesn't work.  Teach __rdfsbase_inactive() and
__wrgsbase_inactive() to use rdmsrl()/wrmsrl() on Xen PV.  The Xen
pvop code will understand this and issue the correct hypercalls.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/f07c08f178fe9711915862b656722a207cd52c28.1593192140.git.luto@kernel.org

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index cb8e37d3acaa42d1ed801484cf3bc3eca261b87c..e14476f0c533afa7794528910a1aee4eb6ad08d8 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -163,9 +163,15 @@ static noinstr unsigned long __rdgsbase_inactive(void)
 
        lockdep_assert_irqs_disabled();
 
-       native_swapgs();
-       gsbase = rdgsbase();
-       native_swapgs();
+       if (!static_cpu_has(X86_FEATURE_XENPV)) {
+               native_swapgs();
+               gsbase = rdgsbase();
+               native_swapgs();
+       } else {
+               instrumentation_begin();
+               rdmsrl(MSR_KERNEL_GS_BASE, gsbase);
+               instrumentation_end();
+       }
 
        return gsbase;
 }
@@ -182,9 +188,15 @@ static noinstr void __wrgsbase_inactive(unsigned long gsbase)
 {
        lockdep_assert_irqs_disabled();
 
-       native_swapgs();
-       wrgsbase(gsbase);
-       native_swapgs();
+       if (!static_cpu_has(X86_FEATURE_XENPV)) {
+               native_swapgs();
+               wrgsbase(gsbase);
+               native_swapgs();
+       } else {
+               instrumentation_begin();
+               wrmsrl(MSR_KERNEL_GS_BASE, gsbase);
+               instrumentation_end();
+       }
 }
 
 /*