linux-kernel - [RFC][PATCH 08/18] x86/xen: Make read

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Message-ID: <20210621120121.048244731@infradead.org>
Date:   Mon, 21 Jun 2021 13:12:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     jpoimboe@...hat.com, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        joro@...tes.org, boris.ostrovsky@...cle.com, jgross@...e.com,
        x86@...nel.org, mbenes@...e.com
Subject: [RFC][PATCH 08/18] x86/xen: Make read_cr2() noinstr

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@...radead.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)