Linux Virtualization - Nov 2017 - [PATCH 03/13] x86/paravirt: Convert native patch assembly code strings to macros

On Wed, Oct 04, 2017 at 10:58:24AM -0500, Josh Poimboeuf
wrote:
> Convert the hard-coded native patch assembly code strings to macros to
> facilitate sharing common code between 32-bit and 64-bit.
> 
> These macros will also be used by a future patch which requires the GCC
> extended asm syntax of two '%' characters instead of one when
specifying
> a register name.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe at redhat.com>
> ---
>  arch/x86/include/asm/special_insns.h | 24 ++++++++++++++++++++++++
>  arch/x86/kernel/paravirt_patch_32.c  | 21 +++++++++++----------
>  arch/x86/kernel/paravirt_patch_64.c  | 29 +++++++++++++++--------------
>  3 files changed, 50 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/x86/include/asm/special_insns.h
b/arch/x86/include/asm/special_insns.h
> index ac402c6fc24b..0549c5f2c1b3 100644
> --- a/arch/x86/include/asm/special_insns.h
> +++ b/arch/x86/include/asm/special_insns.h
> @@ -6,6 +6,30 @@
>  
>  #include <asm/nops.h>
>  
> +#ifdef CONFIG_X86_64
> +# define _REG_ARG1			"%rdi"
> +# define NATIVE_IDENTITY_32		"mov %edi, %eax"
Yeah, that "identity" looks strange. How about NATIVE_NOOP and
NATIVE_NOOP_32 ?
> +# define NATIVE_USERGS_SYSRET64		"swapgs; sysretq"
> +#else
> +# define _REG_ARG1			"%eax"
> +#endif
> +
> +#define _REG_RET			"%" _ASM_AX
> +
> +#define NATIVE_ZERO			"xor " _REG_ARG1 ", " _REG_ARG1
NATIVE_ZERO_OUT

I guess. NATIVE_ZERO reads like the native representation of 0 :-)

...

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

On 17/11/17 19:07, Borislav Petkov wrote:
> On Wed, Oct 04, 2017 at 10:58:24AM -0500, Josh Poimboeuf wrote:
>> Convert the hard-coded native patch assembly code strings to macros to
>> facilitate sharing common code between 32-bit and 64-bit.
>>
>> These macros will also be used by a future patch which requires the GCC
>> extended asm syntax of two '%' characters instead of one when
specifying
>> a register name.
>>
>> Signed-off-by: Josh Poimboeuf <jpoimboe at redhat.com>
>> ---
>>  arch/x86/include/asm/special_insns.h | 24 ++++++++++++++++++++++++
>>  arch/x86/kernel/paravirt_patch_32.c  | 21 +++++++++++----------
>>  arch/x86/kernel/paravirt_patch_64.c  | 29
+++++++++++++++--------------
>>  3 files changed, 50 insertions(+), 24 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/special_insns.h
b/arch/x86/include/asm/special_insns.h
>> index ac402c6fc24b..0549c5f2c1b3 100644
>> --- a/arch/x86/include/asm/special_insns.h
>> +++ b/arch/x86/include/asm/special_insns.h
>> @@ -6,6 +6,30 @@
>>  
>>  #include <asm/nops.h>
>>  
>> +#ifdef CONFIG_X86_64
>> +# define _REG_ARG1			"%rdi"
>> +# define NATIVE_IDENTITY_32		"mov %edi, %eax"
> 
> Yeah, that "identity" looks strange. How about NATIVE_NOOP and
> NATIVE_NOOP_32 ?
Those are not NOPs. They return the identical value which was passed to
them. So identity isn't a bad name after all.
> 
>> +# define NATIVE_USERGS_SYSRET64		"swapgs; sysretq"
>> +#else
>> +# define _REG_ARG1			"%eax"
>> +#endif
>> +
>> +#define _REG_RET			"%" _ASM_AX
>> +
>> +#define NATIVE_ZERO			"xor " _REG_ARG1 ", "
_REG_ARG1
> 
> NATIVE_ZERO_OUT
> 
> I guess. NATIVE_ZERO reads like the native representation of 0 :-)
NATIVE_ZERO_ARG1?


Juergen

On Fri, Nov 17, 2017 at 08:10:13PM +0100, Juergen Gross
wrote:
> On 17/11/17 19:07, Borislav Petkov wrote:
> > On Wed, Oct 04, 2017 at 10:58:24AM -0500, Josh Poimboeuf wrote:
> >> Convert the hard-coded native patch assembly code strings to
macros to
> >> facilitate sharing common code between 32-bit and 64-bit.
> >>
> >> These macros will also be used by a future patch which requires
the GCC
> >> extended asm syntax of two '%' characters instead of one
when specifying
> >> a register name.
> >>
> >> Signed-off-by: Josh Poimboeuf <jpoimboe at redhat.com>
> >> ---
> >>  arch/x86/include/asm/special_insns.h | 24
++++++++++++++++++++++++
> >>  arch/x86/kernel/paravirt_patch_32.c  | 21 +++++++++++----------
> >>  arch/x86/kernel/paravirt_patch_64.c  | 29
+++++++++++++++--------------
> >>  3 files changed, 50 insertions(+), 24 deletions(-)
> >>
> >> diff --git a/arch/x86/include/asm/special_insns.h
b/arch/x86/include/asm/special_insns.h
> >> index ac402c6fc24b..0549c5f2c1b3 100644
> >> --- a/arch/x86/include/asm/special_insns.h
> >> +++ b/arch/x86/include/asm/special_insns.h
> >> @@ -6,6 +6,30 @@
> >>  
> >>  #include <asm/nops.h>
> >>  
> >> +#ifdef CONFIG_X86_64
> >> +# define _REG_ARG1			"%rdi"
> >> +# define NATIVE_IDENTITY_32		"mov %edi, %eax"
> > 
> > Yeah, that "identity" looks strange. How about NATIVE_NOOP
and
> > NATIVE_NOOP_32 ?
> 
> Those are not NOPs. They return the identical value which was passed to
> them. So identity isn't a bad name after all.
Right, like the math identity function:

  https://en.wikipedia.org/wiki/Identity_function
> >> +# define NATIVE_USERGS_SYSRET64		"swapgs; sysretq"
> >> +#else
> >> +# define _REG_ARG1			"%eax"
> >> +#endif
> >> +
> >> +#define _REG_RET			"%" _ASM_AX
> >> +
> >> +#define NATIVE_ZERO			"xor " _REG_ARG1 ", "
_REG_ARG1
> > 
> > NATIVE_ZERO_OUT
> > 
> > I guess. NATIVE_ZERO reads like the native representation of 0 :-)
> 
> NATIVE_ZERO_ARG1?
On a slight tangent, does anybody know why it zeros the arg?

The only place it's used is here:

#if defined(CONFIG_PARAVIRT_SPINLOCKS)
DEF_NATIVE(pv_lock_ops,	queued_spin_unlock,	NATIVE_QUEUED_SPIN_UNLOCK);
DEF_NATIVE(pv_lock_ops,	vcpu_is_preempted,	NATIVE_ZERO);
#endif

Isn't that a bug?  Seems like it should _return_ zero.  Zeroing the arg
shouldn't have any effect.

If I'm right, we could call it NATIVE_FALSE.

-- 
Josh