SWAPGS is used only for interrupts coming from user mode or for
returning to user mode. So there is no reason to use the PARAVIRT
framework, as it can easily be replaced by an ALTERNATIVE depending
on X86_FEATURE_XENPV.
There are several instances using the PV-aware SWAPGS macro in paths
which are never executed in a Xen PV guest. Replace those with the
plain swapgs instruction. For SWAPGS_UNSAFE_STACK the same applies.
Signed-off-by: Juergen Gross
---
arch/x86/entry/entry_64.S | 10 +-
arch/x86/include/asm/irqflags.h | 20
arch/x86/include/asm/paravirt.h | 20
arch/x86/include/asm/paravirt_types.h | 2 --
arch/x86/kernel/asm-offsets_64.c | 1 -
arch/x86/kernel/paravirt.c| 1 -
arch/x86/kernel/paravirt_patch.c | 3 ---
arch/x86/xen/enlighten_pv.c | 3 ---
8 files changed, 13 insertions(+), 47 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index cad08703c4ad..a876204a73e0 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -669,7 +669,7 @@ native_irq_return_ldt:
*/
pushq %rdi/* Stash user RDI */
- SWAPGS /* to kernel GS */
+ swapgs /* to kernel GS */
SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi /* to kernel CR3 */
movqPER_CPU_VAR(espfix_waddr), %rdi
@@ -699,7 +699,7 @@ native_irq_return_ldt:
orq PER_CPU_VAR(espfix_stack), %rax
SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
- SWAPGS /* to user GS */
+ swapgs /* to user GS */
popq%rdi/* Restore user RDI */
movq%rax, %rsp
@@ -943,7 +943,7 @@ SYM_CODE_START_LOCAL(paranoid_entry)
ret
.Lparanoid_entry_swapgs:
- SWAPGS
+ swapgs
/*
* The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an
@@ -1001,7 +1001,7 @@ SYM_CODE_START_LOCAL(paranoid_exit)
jnz restore_regs_and_return_to_kernel
/* We are returning to a context with user GSBASE */
- SWAPGS_UNSAFE_STACK
+ swapgs
jmp restore_regs_and_return_to_kernel
SYM_CODE_END(paranoid_exit)
@@ -1426,7 +1426,7 @@ nmi_no_fsgsbase:
jnz nmi_restore
nmi_swapgs:
- SWAPGS_UNSAFE_STACK
+ swapgs
nmi_restore:
POP_REGS
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index 2dfc8d380dab..8c86edefa115 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -131,18 +131,6 @@ static __always_inline unsigned long
arch_local_irq_save(void)
#define SAVE_FLAGS(x) pushfq; popq %rax
#endif
-#define SWAPGS swapgs
-/*
- * Currently paravirt can't handle swapgs nicely when we
- * don't have a stack we can rely on (such as a user space
- * stack). So we either find a way around these or just fault
- * and emulate if a guest tries to call swapgs directly.
- *
- * Either way, this is a good way to document that we don't
- * have a reliable stack. x86_64 only.
- */
-#define SWAPGS_UNSAFE_STACKswapgs
-
#define INTERRUPT_RETURN jmp native_iret
#define USERGS_SYSRET64\
swapgs; \
@@ -170,6 +158,14 @@ static __always_inline int arch_irqs_disabled(void)
return arch_irqs_disabled_flags(flags);
}
+#else
+#ifdef CONFIG_X86_64
+#ifdef CONFIG_XEN_PV
+#define SWAPGS ALTERNATIVE "swapgs", "", X86_FEATURE_XENPV
+#else
+#define SWAPGS swapgs
+#endif
+#endif
#endif /* !__ASSEMBLY__ */
#endif
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index d25cc6830e89..5647bcdba776 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -776,26 +776,6 @@ extern void default_banner(void);
#ifdef CONFIG_X86_64
#ifdef CONFIG_PARAVIRT_XXL
-/*
- * If swapgs is used while the userspace stack is still current,
- * there's no way to call a pvop. The PV replacement *must* be
- * inlined, or the swapgs instruction must be trapped and emulated.
- */
-#define SWAPGS_UNSAFE_STACK\
- PARA_SITE(PARA_PATCH(PV_CPU_swapgs), swapgs)
-
-/*
- * Note: swapgs is very special, and in practise is either going to be
- * implemented with a single "swapgs" instruction or something very
- * special. Either way, we don't need to save any registers for
- * it.
- */
-#define SWAPGS \
- PARA_SITE(PARA_PATCH(PV_CPU_swapgs),\
- ANNOTATE_RETPOLINE_SAFE; \
- call PARA_INDIRECT(pv_ops+PV_CPU_swapgs); \
-)
-
#define USERGS_SYSRET64
