x86/paravirt: add sysret/sysexit pvops for returning to 32-bit compatibility userspace

In a 64-bit system, we need separate sysret/sysexit operations to
return to a 32-bit userspace.

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>

2 files changed, 56 insertions, 14 deletions

diff --git a/include/asm-x86/irqflags.h b/include/asm-x86/irqflags.h
index 544836c96b61..ea9bd2635d59 100644
--- a/include/asm-x86/irqflags.h
+++ b/include/asm-x86/irqflags.h
@@ -112,9 +112,17 @@ static inline unsigned long __raw_local_irq_save(void)
 
 #ifdef CONFIG_X86_64
 #define INTERRUPT_RETURN        iretq
-#define USERGS_SYSRET                                   \
-                        swapgs;                         \
-                        sysretq;
+#define USERGS_SYSRET64                         \
+        swapgs;                                 \
+        sysretq;
+#define USERGS_SYSRET32                         \
+        swapgs;                                 \
+        sysretl
+#define ENABLE_INTERRUPTS_SYSEXIT32             \
+        swapgs;                                 \
+        sti;                                    \
+        sysexit
+
 #else
 #define INTERRUPT_RETURN                iret
 #define ENABLE_INTERRUPTS_SYSEXIT       sti; sysexit
diff --git a/include/asm-x86/paravirt.h b/include/asm-x86/paravirt.h
index dad5b4186f51..33f72f8fe757 100644
--- a/include/asm-x86/paravirt.h
+++ b/include/asm-x86/paravirt.h
@@ -141,9 +141,32 @@ struct pv_cpu_ops {
         u64 (*read_pmc)(int counter);
         unsigned long long (*read_tscp)(unsigned int *aux);
 
-        /* These three are jmp to, not actually called. */
+        /*
+         * Atomically enable interrupts and return to userspace.  This
+         * is only ever used to return to 32-bit processes; in a
+         * 64-bit kernel, it's used for 32-on-64 compat processes, but
+         * never native 64-bit processes.  (Jump, not call.)
+         */
         void (*irq_enable_sysexit)(void);
-        void (*usergs_sysret)(void);
+
+        /*
+         * Switch to usermode gs and return to 64-bit usermode using
+         * sysret.  Only used in 64-bit kernels to return to 64-bit
+         * processes.  Usermode register state, including %rsp, must
+         * already be restored.
+         */
+        void (*usergs_sysret64)(void);
+
+        /*
+         * Switch to usermode gs and return to 32-bit usermode using
+         * sysret.  Used to return to 32-on-64 compat processes.
+         * Other usermode register state, including %esp, must already
+         * be restored.
+         */
+        void (*usergs_sysret32)(void);
+
+        /* Normal iret.  Jump to this with the standard iret stack
+           frame set up. */
         void (*iret)(void);
 
         void (*swapgs)(void);
@@ -1481,18 +1504,24 @@ 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_SYSEXIT                                       \
-        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_irq_enable_sysexit),    \
+#define USERGS_SYSRET32                                                 \
+        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret32),       \
                   CLBR_NONE,                                            \
-                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_irq_enable_sysexit))
-
+                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usergs_sysret32))
 
 #ifdef CONFIG_X86_32
 #define GET_CR0_INTO_EAX                                \
         push %ecx; push %edx;                           \
         call PARA_INDIRECT(pv_cpu_ops+PV_CPU_read_cr0); \
         pop %edx; pop %ecx
-#else
+
+#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_sysexit))
+
+
+#else   /* !CONFIG_X86_32 */
 #define SWAPGS                                                          \
         PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE,     \
                   PV_SAVE_REGS;                                         \
@@ -1505,11 +1534,16 @@ static inline unsigned long __raw_local_irq_save(void)
         movq %rax, %rcx;                                \
         xorq %rax, %rax;
 
-#define USERGS_SYSRET                                                   \
-        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret),         \
+#define USERGS_SYSRET64                                                 \
+        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret64),       \
                   CLBR_NONE,                                            \
-                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usergs_sysret))
-#endif
+                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usergs_sysret64))
+
+#define ENABLE_INTERRUPTS_SYSEXIT32                                     \
+        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_irq_enable_sysexit),    \
+                  CLBR_NONE,                                            \
+                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_irq_enable_sysexit))
+#endif  /* CONFIG_X86_32 */
 
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_PARAVIRT */