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Subject[PATCH v4 11/45] x86/entry,xen: Early rewrite of restore_regs_and_return_to_kernel()
By doing an early rewrite of 'jmp native_iret` in
restore_regs_and_return_to_kernel() we can get rid of the last
INTERRUPT_RETURN user and paravirt_iret.

Suggested-by: Andrew Cooper <Andrew.Cooper3@citrix.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/entry/entry_64.S | 11 ++++++++---
arch/x86/include/asm/irqflags.h | 5 -----
arch/x86/include/asm/paravirt_types.h | 1 -
arch/x86/kernel/head_64.S | 3 ++-
arch/x86/kernel/paravirt.c | 4 ----
arch/x86/xen/enlighten_pv.c | 7 ++++++-
arch/x86/xen/xen-asm.S | 1 +
7 files changed, 17 insertions(+), 15 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -609,7 +609,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_
/* Restore RDI. */
popq %rdi
swapgs
- jmp native_iret
+ jmp .Lnative_iret


SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)
@@ -626,9 +626,14 @@ SYM_INNER_LABEL(restore_regs_and_return_
* ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization
* when returning from IPI handler.
*/
- INTERRUPT_RETURN
+#ifdef CONFIG_XEN_PV
+SYM_INNER_LABEL(early_xen_iret_patch, SYM_L_GLOBAL)
+ ANNOTATE_NOENDBR
+ .byte 0xe9
+ .long .Lnative_iret - (. + 4)
+#endif

-SYM_INNER_LABEL_ALIGN(native_iret, SYM_L_GLOBAL)
+.Lnative_iret:
UNWIND_HINT_IRET_REGS
/*
* Are we returning to a stack segment from the LDT? Note: in
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -141,13 +141,8 @@ static __always_inline void arch_local_i
#ifdef CONFIG_X86_64
#ifdef CONFIG_XEN_PV
#define SWAPGS ALTERNATIVE "swapgs", "", X86_FEATURE_XENPV
-#define INTERRUPT_RETURN \
- ANNOTATE_RETPOLINE_SAFE; \
- ALTERNATIVE_TERNARY("jmp *paravirt_iret(%rip);", \
- X86_FEATURE_XENPV, "jmp xen_iret;", "jmp native_iret;")
#else
#define SWAPGS swapgs
-#define INTERRUPT_RETURN jmp native_iret
#endif
#endif
#endif /* !__ASSEMBLY__ */
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -272,7 +272,6 @@ struct paravirt_patch_template {

extern struct pv_info pv_info;
extern struct paravirt_patch_template pv_ops;
-extern void (*paravirt_iret)(void);

#define PARAVIRT_PATCH(x) \
(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -345,7 +345,6 @@ SYM_CODE_START_NOALIGN(vc_boot_ghcb)
/* Remove Error Code */
addq $8, %rsp

- /* Pure iret required here - don't use INTERRUPT_RETURN */
iretq
SYM_CODE_END(vc_boot_ghcb)
#endif
@@ -426,6 +425,8 @@ SYM_CODE_END(early_idt_handler_common)
* early_idt_handler_array can't be used because it returns via the
* paravirtualized INTERRUPT_RETURN and pv-ops don't work that early.
*
+ * XXX it does, fix this.
+ *
* This handler will end up in the .init.text section and not be
* available to boot secondary CPUs.
*/
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -132,8 +132,6 @@ void paravirt_set_sched_clock(u64 (*func
}

/* These are in entry.S */
-extern void native_iret(void);
-
static struct resource reserve_ioports = {
.start = 0,
.end = IO_SPACE_LIMIT,
@@ -397,8 +395,6 @@ struct paravirt_patch_template pv_ops =

#ifdef CONFIG_PARAVIRT_XXL
NOKPROBE_SYMBOL(native_load_idt);
-
-void (*paravirt_iret)(void) = native_iret;
#endif

EXPORT_SYMBOL(pv_ops);
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1177,6 +1177,8 @@ static void __init xen_domu_set_legacy_f
x86_platform.legacy.rtc = 0;
}

+extern void early_xen_iret_patch(void);
+
/* First C function to be called on Xen boot */
asmlinkage __visible void __init xen_start_kernel(void)
{
@@ -1187,6 +1189,10 @@ asmlinkage __visible void __init xen_sta
if (!xen_start_info)
return;

+ __text_gen_insn(&early_xen_iret_patch,
+ JMP32_INSN_OPCODE, &early_xen_iret_patch, &xen_iret,
+ JMP32_INSN_SIZE);
+
xen_domain_type = XEN_PV_DOMAIN;
xen_start_flags = xen_start_info->flags;

@@ -1195,7 +1201,6 @@ asmlinkage __visible void __init xen_sta
/* Install Xen paravirt ops */
pv_info = xen_info;
pv_ops.cpu = xen_cpu_ops.cpu;
- paravirt_iret = xen_iret;
xen_init_irq_ops();

/*
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -189,6 +189,7 @@ hypercall_iret = hypercall_page + __HYPE
*/
SYM_CODE_START(xen_iret)
UNWIND_HINT_EMPTY
+ ANNOTATE_NOENDBR
pushq $0
jmp hypercall_iret
SYM_CODE_END(xen_iret)

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