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>

7 files changed, 89 insertions, 31 deletions

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 3aefbce2de48..2a4c42427d9a 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -61,6 +61,19 @@
         CFI_UNDEFINED   r15
         .endm
 
+#ifdef CONFIG_PARAVIRT
+ENTRY(native_usergs_sysret32)
+        swapgs
+        sysretl
+ENDPROC(native_usergs_sysret32)
+
+ENTRY(native_irq_enable_sysexit)
+        swapgs
+        sti
+        sysexit
+ENDPROC(native_irq_enable_sysexit)
+#endif
+
 /*
  * 32bit SYSENTER instruction entry.
  *
@@ -151,10 +164,7 @@ sysenter_do_call:
         CFI_ADJUST_CFA_OFFSET -8
         CFI_REGISTER rsp,rcx
         TRACE_IRQS_ON
-        swapgs
-        sti             /* sti only takes effect after the next instruction */
-        /* sysexit */
-        .byte   0xf, 0x35
+        ENABLE_INTERRUPTS_SYSEXIT32
 
 sysenter_tracesys:
         CFI_RESTORE_STATE
@@ -254,8 +264,7 @@ cstar_do_call:
         TRACE_IRQS_ON
         movl RSP-ARGOFFSET(%rsp),%esp
         CFI_RESTORE rsp
-        swapgs
-        sysretl
+        USERGS_SYSRET32
         
 cstar_tracesys: 
         CFI_RESTORE_STATE
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index a19aba8c5bb3..06c451af979a 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -62,7 +62,9 @@ int main(void)
         OFFSET(PV_IRQ_irq_disable, pv_irq_ops, irq_disable);
         OFFSET(PV_IRQ_irq_enable, pv_irq_ops, irq_enable);
         OFFSET(PV_CPU_iret, pv_cpu_ops, iret);
-        OFFSET(PV_CPU_usergs_sysret, pv_cpu_ops, usergs_sysret);
+        OFFSET(PV_CPU_usergs_sysret32, pv_cpu_ops, usergs_sysret32);
+        OFFSET(PV_CPU_usergs_sysret64, pv_cpu_ops, usergs_sysret64);
+        OFFSET(PV_CPU_irq_enable_sysexit, pv_cpu_ops, irq_enable_sysexit);
         OFFSET(PV_CPU_swapgs, pv_cpu_ops, swapgs);
         OFFSET(PV_MMU_read_cr2, pv_mmu_ops, read_cr2);
 #endif
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 18447a373fbd..880ffe510a11 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -59,7 +59,7 @@
 #endif  
 
 #ifdef CONFIG_PARAVIRT
-ENTRY(native_usergs_sysret)
+ENTRY(native_usergs_sysret64)
         swapgs
         sysretq
 #endif /* CONFIG_PARAVIRT */
@@ -275,7 +275,7 @@ sysret_check:
         RESTORE_ARGS 0,-ARG_SKIP,1
         /*CFI_REGISTER  rflags,r11*/
         movq    %gs:pda_oldrsp, %rsp
-        USERGS_SYSRET
+        USERGS_SYSRET64
 
         CFI_RESTORE_STATE
         /* Handle reschedules */
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index b0b17f0bc7e9..bf1067e89cad 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -141,7 +141,8 @@ unsigned paravirt_patch_default(u8 type, u16 clobbers, void *insnbuf,
                 ret = paravirt_patch_nop();
         else if (type == PARAVIRT_PATCH(pv_cpu_ops.iret) ||
                  type == PARAVIRT_PATCH(pv_cpu_ops.irq_enable_sysexit) ||
-                 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret))
+                 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret32) ||
+                 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret64))
                 /* If operation requires a jmp, then jmp */
                 ret = paravirt_patch_jmp(insnbuf, opfunc, addr, len);
         else
@@ -193,7 +194,8 @@ static void native_flush_tlb_single(unsigned long addr)
 /* These are in entry.S */
 extern void native_iret(void);
 extern void native_irq_enable_sysexit(void);
-extern void native_usergs_sysret(void);
+extern void native_usergs_sysret32(void);
+extern void native_usergs_sysret64(void);
 
 static int __init print_banner(void)
 {
@@ -329,10 +331,10 @@ struct pv_cpu_ops pv_cpu_ops = {
         .write_idt_entry = native_write_idt_entry,
         .load_sp0 = native_load_sp0,
 
-#ifdef CONFIG_X86_32
         .irq_enable_sysexit = native_irq_enable_sysexit,
-#else
-        .usergs_sysret = native_usergs_sysret,
+#ifdef CONFIG_X86_64
+        .usergs_sysret32 = native_usergs_sysret32,
+        .usergs_sysret64 = native_usergs_sysret64,
 #endif
         .iret = native_iret,
         .swapgs = native_swapgs,
diff --git a/arch/x86/kernel/paravirt_patch_64.c b/arch/x86/kernel/paravirt_patch_64.c
index d4c0712a3e64..061d01df9ae6 100644
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -14,8 +14,9 @@ DEF_NATIVE(pv_mmu_ops, flush_tlb_single, "invlpg (%rdi)");
 DEF_NATIVE(pv_cpu_ops, clts, "clts");
 DEF_NATIVE(pv_cpu_ops, wbinvd, "wbinvd");
 
-/* the three commands give us more control to how to return from a syscall */
-DEF_NATIVE(pv_cpu_ops, usergs_sysret, "swapgs; sysretq;");
+DEF_NATIVE(pv_cpu_ops, irq_enable_sysexit, "swapgs; sti; sysexit");
+DEF_NATIVE(pv_cpu_ops, usergs_sysret64, "swapgs; sysretq");
+DEF_NATIVE(pv_cpu_ops, usergs_sysret32, "swapgs; sysretl");
 DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs");
 
 unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
@@ -35,7 +36,9 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
                 PATCH_SITE(pv_irq_ops, irq_enable);
                 PATCH_SITE(pv_irq_ops, irq_disable);
                 PATCH_SITE(pv_cpu_ops, iret);
-                PATCH_SITE(pv_cpu_ops, usergs_sysret);
+                PATCH_SITE(pv_cpu_ops, irq_enable_sysexit);
+                PATCH_SITE(pv_cpu_ops, usergs_sysret32);
+                PATCH_SITE(pv_cpu_ops, usergs_sysret64);
                 PATCH_SITE(pv_cpu_ops, swapgs);
                 PATCH_SITE(pv_mmu_ops, read_cr2);
                 PATCH_SITE(pv_mmu_ops, read_cr3);
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 */