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Re: [PATCH v2 2/2] x86/spec: adjust logic to logic that elides lfence
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 22 Apr 2024 15:59:48 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 22 Apr 2024 13:59:59 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22.04.2024 15:35, Roger Pau Monné wrote:
> On Fri, Apr 19, 2024 at 08:25:00AM +0200, Jan Beulich wrote:
>> On 18.04.2024 17:52, Roger Pau Monne wrote:
>>> --- a/xen/arch/x86/include/asm/cpufeature.h
>>> +++ b/xen/arch/x86/include/asm/cpufeature.h
>>> @@ -235,9 +235,6 @@ static inline bool boot_cpu_has(unsigned int feat)
>>> #define cpu_bug_fpu_ptrs boot_cpu_has(X86_BUG_FPU_PTRS)
>>> #define cpu_bug_null_seg boot_cpu_has(X86_BUG_NULL_SEG)
>>>
>>> -#define cpu_has_bhb_seq (boot_cpu_has(X86_SPEC_BHB_TSX) || \
>>> - boot_cpu_has(X86_SPEC_BHB_LOOPS))
>>
>> Might be worth also mentioning in the description that this construct was
>> lacking use of X86_SPEC_BHB_LOOPS_LONG (might even warrant a 2nd Fixes:
>> tag).
>
> Heh, no, X86_SPEC_BHB_LOOPS_LONG is added in addition to
> X86_SPEC_BHB_LOOPS. When using long loops we have both
> X86_SPEC_BHB_LOOPS and X86_SPEC_BHB_LOOPS_LONG set (I know it's
> confusing, I was also confused the first time and asked Andrew the
> same question). See the fallthrough in bhi_calculations().
Oh, I see.
Andrew: This is a very good example of the separating blank line being
misleading when fall-through is intended.
Jan
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