Re: [PATCH v2 2/4] VMX: move various uses of UD2 out of fast paths

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 26/08/2013 09:58, Jan Beulich wrote:
> ... at once making conditional forward jumps, which are statically
> predicted to be not taken, only used for the unlikely (error) cases.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

> ---
> v2: Fix #UD recovery for INVVPID (unintended flow change spotted by Andrew Cooper).
>
> --- a/xen/include/asm-x86/asm_defns.h
> +++ b/xen/include/asm-x86/asm_defns.h
> @@ -67,6 +67,30 @@ void ret_from_intr(void);
>  #define ASSERT_NOT_IN_ATOMIC
>  #endif
>  
> +#else
> +
> +#ifdef __clang__ /* clang's builtin assember can't do .subsection */
> +
> +#define UNLIKELY_START_SECTION ".pushsection .fixup,\"ax\""
> +#define UNLIKELY_END_SECTION   ".popsection"
> +
> +#else
> +
> +#define UNLIKELY_START_SECTION ".subsection 1"
> +#define UNLIKELY_END_SECTION   ".subsection 0"
> +
> +#endif
> +
> +#define UNLIKELY_START(cond, tag)          \
> +        "j" #cond " .Lunlikely%=.tag;\n\t" \
> +        UNLIKELY_START_SECTION "\n"        \
> +        ".Lunlikely%=.tag:"
> +
> +#define UNLIKELY_END(tag)                  \
> +        "jmp .Llikely%=.tag;\n\t"          \
> +        UNLIKELY_END_SECTION "\n"          \
> +        ".Llikely%=.tag:"
> +
>  #endif
>  
>  #endif /* __X86_ASM_DEFNS_H__ */
> --- a/xen/include/asm-x86/hvm/vmx/vmx.h
> +++ b/xen/include/asm-x86/hvm/vmx/vmx.h
> @@ -285,7 +285,9 @@ static inline void __vmptrld(u64 addr)
>      asm volatile ( VMPTRLD_OPCODE
>                     MODRM_EAX_06
>                     /* CF==1 or ZF==1 --> crash (ud2) */
> -                   "ja 1f ; ud2 ; 1:\n"
> +                   UNLIKELY_START(be, vmptrld)
> +                   "\tud2\n"
> +                   UNLIKELY_END_SECTION
>                     :
>                     : "a" (&addr)
>                     : "memory");
> @@ -296,7 +298,9 @@ static inline void __vmpclear(u64 addr)
>      asm volatile ( VMCLEAR_OPCODE
>                     MODRM_EAX_06
>                     /* CF==1 or ZF==1 --> crash (ud2) */
> -                   "ja 1f ; ud2 ; 1:\n"
> +                   UNLIKELY_START(be, vmclear)
> +                   "\tud2\n"
> +                   UNLIKELY_END_SECTION
>                     :
>                     : "a" (&addr)
>                     : "memory");
> @@ -309,7 +313,9 @@ static inline unsigned long __vmread(uns
>      asm volatile ( VMREAD_OPCODE
>                     MODRM_EAX_ECX
>                     /* CF==1 or ZF==1 --> crash (ud2) */
> -                   "ja 1f ; ud2 ; 1:\n"
> +                   UNLIKELY_START(be, vmread)
> +                   "\tud2\n"
> +                   UNLIKELY_END_SECTION
>                     : "=c" (ecx)
>                     : "a" (field)
>                     : "memory");
> @@ -322,7 +328,9 @@ static inline void __vmwrite(unsigned lo
>      asm volatile ( VMWRITE_OPCODE
>                     MODRM_EAX_ECX
>                     /* CF==1 or ZF==1 --> crash (ud2) */
> -                   "ja 1f ; ud2 ; 1:\n"
> +                   UNLIKELY_START(be, vmwrite)
> +                   "\tud2\n"
> +                   UNLIKELY_END_SECTION
>                     : 
>                     : "a" (field) , "c" (value)
>                     : "memory");
> @@ -360,7 +368,9 @@ static inline void __invept(int type, u6
>      asm volatile ( INVEPT_OPCODE
>                     MODRM_EAX_08
>                     /* CF==1 or ZF==1 --> crash (ud2) */
> -                   "ja 1f ; ud2 ; 1:\n"
> +                   UNLIKELY_START(be, invept)
> +                   "\tud2\n"
> +                   UNLIKELY_END_SECTION
>                     :
>                     : "a" (&operand), "c" (type)
>                     : "memory" );
> @@ -377,7 +387,10 @@ static inline void __invvpid(int type, u
>      /* Fix up #UD exceptions which occur when TLBs are flushed before VMXON. */
>      asm volatile ( "1: " INVVPID_OPCODE MODRM_EAX_08
>                     /* CF==1 or ZF==1 --> crash (ud2) */
> -                   "ja 2f ; ud2 ; 2:\n"
> +                   UNLIKELY_START(be, invvpid)
> +                   "\tud2\n"
> +                   UNLIKELY_END_SECTION "\n"
> +                   "2:"
>                     _ASM_EXTABLE(1b, 2b)
>                     :
>                     : "a" (&operand), "c" (type)
>
>
>
>
>
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