linux-kernel - [RFC PATCH 71/73] x86/pvm: Adapt pushf/popf in this_cpu_cmpxchg16b

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Date: Mon, 26 Feb 2024 22:36:28 +0800
From: Lai Jiangshan <jiangshanlai@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Hou Wenlong <houwenlong.hwl@...group.com>,
	Lai Jiangshan <jiangshan.ljs@...group.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...hat.com>,
	kvm@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	x86@...nel.org,
	Kees Cook <keescook@...omium.org>,
	Juergen Gross <jgross@...e.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [RFC PATCH 71/73] x86/pvm: Adapt pushf/popf in this_cpu_cmpxchg16b_emu()

From: Hou Wenlong <houwenlong.hwl@...group.com>

The pushf/popf instructions in this_cpu_cmpxchg16b_emu() are
non-privilege instructions, so they cannot be trapped and emulated,
which could cause a boot failure. However, since the cmpxchg16b
instruction is supported for PVM guest. we can patch
this_cpu_cmpxchg16b_emu() and use cmpxchg16b directly.

Suggested-by: Lai Jiangshan <jiangshan.ljs@...group.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 arch/x86/kernel/pvm.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/x86/kernel/pvm.c b/arch/x86/kernel/pvm.c
index 1dc2c0fb7daa..567ea19d569c 100644
--- a/arch/x86/kernel/pvm.c
+++ b/arch/x86/kernel/pvm.c
@@ -413,6 +413,34 @@ __visible noinstr void pvm_event(struct pt_regs *regs)
 		common_interrupt(regs, vector);
 }
 
+asm (
+	".pushsection .rodata				\n"
+	".global pvm_cmpxchg16b_emu_template		\n"
+	"pvm_cmpxchg16b_emu_template:			\n"
+	"	cmpxchg16b %gs:(%rsi)			\n"
+	"	ret					\n"
+	".global pvm_cmpxchg16b_emu_tail		\n"
+	"pvm_cmpxchg16b_emu_tail:			\n"
+	".popsection					\n"
+);
+
+extern u8 this_cpu_cmpxchg16b_emu[];
+extern u8 pvm_cmpxchg16b_emu_template[];
+extern u8 pvm_cmpxchg16b_emu_tail[];
+
+static void __init pvm_early_patch(void)
+{
+	/*
+	 * The pushf/popf instructions in this_cpu_cmpxchg16b_emu() are
+	 * non-privilege instructions, so they cannot be trapped and emulated,
+	 * which could cause a boot failure. However, since the cmpxchg16b
+	 * instruction is supported for PVM guest. we can patch
+	 * this_cpu_cmpxchg16b_emu() and use cmpxchg16b directly.
+	 */
+	memcpy(this_cpu_cmpxchg16b_emu, pvm_cmpxchg16b_emu_template,
+	       (unsigned int)(pvm_cmpxchg16b_emu_tail - pvm_cmpxchg16b_emu_template));
+}
+
 extern void pvm_early_kernel_event_entry(void);
 
 /*
@@ -457,6 +485,8 @@ void __init pvm_early_setup(void)
 	wrmsrl(MSR_PVM_EVENT_ENTRY, (unsigned long)(void *)pvm_early_kernel_event_entry - 256);
 	wrmsrl(MSR_PVM_SUPERVISOR_REDZONE, PVM_SUPERVISOR_REDZONE_SIZE);
 	wrmsrl(MSR_PVM_RETS_RIP, (unsigned long)(void *)pvm_rets_rip);
+
+	pvm_early_patch();
 }
 
 void pvm_setup_event_handling(void)
-- 
2.19.1.6.gb485710b