[PATCH v2 14/24] x86/xen: Make read_cr2() noinstr

Peter Zijlstra
2021-06-24T09:56:47Z

vmlinux.o: warning: objtool: pv_ops[41]: native_read_cr2
vmlinux.o: warning: objtool: pv_ops[41]: xen_read_cr2
vmlinux.o: warning: objtool: pv_ops[41]: xen_read_cr2_direct
vmlinux.o: warning: objtool: exc_double_fault()+0x15: call to pv_ops[41]() leaves .noinstr.text section

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/paravirt.h | 2 +-
arch/x86/kernel/paravirt.c | 7 ++++++-
arch/x86/xen/xen-asm.S | 2 ++
3 files changed, 9 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -133,7 +133,7 @@ static inline void write_cr0(unsigned lo
PVOP_VCALL1(cpu.write_cr0, x);
}

-static inline unsigned long read_cr2(void)
+static __always_inline unsigned long read_cr2(void)
{
return PVOP_ALT_CALLEE0(unsigned long, mmu.read_cr2,
"mov %%cr2, %%rax;",
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -238,6 +238,11 @@ struct pv_info pv_info = {
/* 64-bit pagetable entries */
#define PTE_IDENT __PV_IS_CALLEE_SAVE(_paravirt_ident_64)

+static noinstr unsigned long pv_native_read_cr2(void)
+{
+ return native_read_cr2();
+}
+
struct paravirt_patch_template pv_ops = {
/* Cpu ops. */
.cpu.io_delay = native_io_delay,
@@ -298,7 +303,7 @@ struct paravirt_patch_template pv_ops =
.mmu.exit_mmap = paravirt_nop,

#ifdef CONFIG_PARAVIRT_XXL
- .mmu.read_cr2 = __PV_IS_CALLEE_SAVE(native_read_cr2),
+ .mmu.read_cr2 = __PV_IS_CALLEE_SAVE(pv_native_read_cr2),
.mmu.write_cr2 = native_write_cr2,
.mmu.read_cr3 = __native_read_cr3,
.mmu.write_cr3 = native_write_cr3,
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -102,6 +102,7 @@ SYM_FUNC_START(check_events)
ret
SYM_FUNC_END(check_events)

+.pushsection .noinstr.text, "ax"
SYM_FUNC_START(xen_read_cr2)
FRAME_BEGIN
_ASM_MOV PER_CPU_VAR(xen_vcpu), %_ASM_AX
@@ -116,6 +117,7 @@ SYM_FUNC_START(xen_read_cr2_direct)
FRAME_END
ret
SYM_FUNC_END(xen_read_cr2_direct);
+.popsection

.macro xen_pv_trap name
SYM_CODE_START(xen_\name)