x86/paravirt: split sysret and sysexit

Don't conflate sysret and sysexit; they're different instructions with
different semantics, and may be in use at the same time (at least
within the same kernel, depending on whether its an Intel or AMD
system).

sysexit - just return to userspace, does no register restoration of
    any kind; must explicitly atomically enable interrupts.

sysret - reloads flags from r11, so no need to explicitly enable
    interrupts on 64-bit, responsible for restoring usermode %gs

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citirx.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 5 deletions

diff --git a/include/asm-x86/paravirt.h b/include/asm-x86/paravirt.h
index 82cdcde4b222..2668903b70f5 100644
--- a/include/asm-x86/paravirt.h
+++ b/include/asm-x86/paravirt.h
@@ -141,8 +141,9 @@ struct pv_cpu_ops {
         u64 (*read_pmc)(int counter);
         unsigned long long (*read_tscp)(unsigned int *aux);
 
-        /* These two are jmp to, not actually called. */
-        void (*irq_enable_syscall_ret)(void);
+        /* These three are jmp to, not actually called. */
+        void (*irq_enable_sysexit)(void);
+        void (*usersp_sysret)(void);
         void (*iret)(void);
 
         void (*swapgs)(void);
@@ -1480,10 +1481,10 @@ static inline unsigned long __raw_local_irq_save(void)
                   call PARA_INDIRECT(pv_irq_ops+PV_IRQ_irq_enable);     \
                   PV_RESTORE_REGS;)
 
-#define ENABLE_INTERRUPTS_SYSCALL_RET                                   \
-        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_irq_enable_syscall_ret),\
+#define ENABLE_INTERRUPTS_SYSEXIT                                       \
+        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_irq_enable_sysexit),    \
                   CLBR_NONE,                                            \
-                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_irq_enable_syscall_ret))
+                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_irq_enable_sysexit))
 
 
 #ifdef CONFIG_X86_32
@@ -1504,6 +1505,10 @@ static inline unsigned long __raw_local_irq_save(void)
         movq %rax, %rcx;                                \
         xorq %rax, %rax;
 
+#define USERSP_SYSRET                                                   \
+        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usersp_sysret),         \
+                  CLBR_NONE,                                            \
+                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usersp_sysret))
 #endif
 
 #endif /* __ASSEMBLY__ */