Re: [PATCH v10 03/38] x86/msr: Add the WRMSRNS instruction support

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On 14.09.23 06:47, Xin Li wrote:
Add an always inline API __wrmsrns() to embed the WRMSRNS instruction
into the code.

Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>

In order to avoid having to add paravirt support for WRMSRNS I think
xen_init_capabilities() should gain:

+	setup_clear_cpu_cap(X86_FEATURE_WRMSRNS);


Juergen

---
  arch/x86/include/asm/msr.h | 18 ++++++++++++++++++
  1 file changed, 18 insertions(+)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 65ec1965cd28..c284ff9ebe67 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -97,6 +97,19 @@ static __always_inline void __wrmsr(unsigned int msr, u32 low, u32 high)
  		     : : "c" (msr), "a"(low), "d" (high) : "memory");
  }
+/*
+ * WRMSRNS behaves exactly like WRMSR with the only difference being
+ * that it is not a serializing instruction by default.
+ */
+static __always_inline void __wrmsrns(u32 msr, u32 low, u32 high)
+{
+	/* Instruction opcode for WRMSRNS; supported in binutils >= 2.40. */
+	asm volatile("1: .byte 0x0f,0x01,0xc6\n"
+		     "2:\n"
+		     _ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_WRMSR)
+		     : : "c" (msr), "a"(low), "d" (high));
+}
+
  #define native_rdmsr(msr, val1, val2)			\
  do {							\
  	u64 __val = __rdmsr((msr));			\
@@ -297,6 +310,11 @@ do {							\
#endif /* !CONFIG_PARAVIRT_XXL */ +static __always_inline void wrmsrns(u32 msr, u64 val)
+{
+	__wrmsrns(msr, val, val >> 32);
+}
+
  /*
   * 64-bit version of wrmsr_safe():
   */

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