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Re: [PATCH v2 2/4] xen/arm: Add sb instruction support
- To: Julien Grall <julien@xxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Mon, 13 Jun 2022 09:21:35 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Mon, 13 Jun 2022 09:21:58 +0000
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- Thread-topic: [PATCH v2 2/4] xen/arm: Add sb instruction support
Hi Julien,
> On 10 Jun 2022, at 19:20, Julien Grall <julien@xxxxxxx> wrote:
>
> Hi Bertrand,
>
> On 31/05/2022 11:43, Bertrand Marquis wrote:
>> diff --git a/xen/arch/arm/include/asm/cpufeature.h
>> b/xen/arch/arm/include/asm/cpufeature.h
>> index f7368766c0..9649a7afee 100644
>> --- a/xen/arch/arm/include/asm/cpufeature.h
>> +++ b/xen/arch/arm/include/asm/cpufeature.h
>> @@ -67,8 +67,9 @@
>> #define ARM_WORKAROUND_BHB_LOOP_24 13
>> #define ARM_WORKAROUND_BHB_LOOP_32 14
>> #define ARM_WORKAROUND_BHB_SMCC_3 15
>> +#define ARM64_HAS_SB 16
>
> The feature is for both 32-bit and 64-bit. So I would prefer if it is called
> ARM_HAS_SB.
Right make sense.
>
>> -#define ARM_NCAPS 16
>> +#define ARM_NCAPS 17
>> #ifndef __ASSEMBLY__
>> @@ -78,6 +79,9 @@
>> extern DECLARE_BITMAP(cpu_hwcaps, ARM_NCAPS);
>> +void check_local_cpu_features(void);
>> +void enable_cpu_features(void);
>> +
>> static inline bool cpus_have_cap(unsigned int num)
>> {
>> if ( num >= ARM_NCAPS )
>> diff --git a/xen/arch/arm/include/asm/macros.h
>> b/xen/arch/arm/include/asm/macros.h
>> index 1aa373760f..33e863d982 100644
>> --- a/xen/arch/arm/include/asm/macros.h
>> +++ b/xen/arch/arm/include/asm/macros.h
>> @@ -5,14 +5,7 @@
>> # error "This file should only be included in assembly file"
>> #endif
>> - /*
>> - * Speculative barrier
>> - * XXX: Add support for the 'sb' instruction
>> - */
>> - .macro sb
>> - dsb nsh
>> - isb
>> - .endm
>
> Looking at the patch bcab2ac84931 "xen/arm64: Place a speculation barrier
> following an ret instruction", the macro was defined before including
> <asm/arm*/macros.h> so 'sb' could be used in macros defined by the headers.
>
> I can't remember whether I chose the order because I had a failure on some
> compilers. However, I couldn't find anything in the assembler documentation
> suggesting that a macro A could use B before it is used.
>
> So I would rather avoid to move the macro if there are no strong argument for
> it.
Sure I will put it back where it was.
Cheers
Bertrand
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