Re: [PATCH 5/6] riscv: hwprobe: Report XTheadVector only when available

[Radim Krčmář]

2026-10-06T16:54:53-07:00, Charlie Jenkins <thecharlesjenkins@xxxxxxxxx>:
>> User-mode use of XTheadVector requires non-Off sstatus.VS, which we set
>> only when has_xtheadvector() (CONFIG_RISCV_ISA_XTHEADVECTOR and
>> XTheadVector on all harts).  XTheadVector also bundles operations with
>> floating state, which additionally requires non-Off sstatus.FS and hence
>> has_fpu().  hwprobe reports XTheadVector from the per-hart vendor ISA
>> bitmaps alone, so it can advertise an extension that is always disabled
>> in user-mode.
>> 
>> Report correct environment to user-mode.
>> 
>> Fixes: a5ea53da65c5 ("riscv: hwprobe: Add thead vendor extension probing")
>> Signed-off-by: Radim Krčmář <radim.krcmar@xxxxxxxxxxxxxxxx>
>>
>> diff --git a/arch/riscv/kernel/vendor_extensions/thead_hwprobe.c b/arch/riscv/kernel/vendor_extensions/thead_hwprobe.c
>> index 2eba34011786..f07aa1c8acac 100644
>> --- a/arch/riscv/kernel/vendor_extensions/thead_hwprobe.c
>> +++ b/arch/riscv/kernel/vendor_extensions/thead_hwprobe.c
>> @@ -1,5 +1,7 @@
>>  // SPDX-License-Identifier: GPL-2.0-only
>>  
>> +#include <asm/switch_to.h>
>> +#include <asm/vector.h>
>>  #include <asm/vendor_extensions/thead.h>
>>  #include <asm/vendor_extensions/thead_hwprobe.h>
>>  #include <asm/vendor_extensions/vendor_hwprobe.h>
>> @@ -14,6 +16,7 @@ void hwprobe_isa_vendor_ext_thead_0(struct riscv_hwprobe *pair, const struct cpu
>>  {
>>  	VENDOR_EXTENSION_SUPPORTED(pair, cpus,
>>  				   riscv_isa_vendor_ext_list_thead.per_hart_isa_bitmap, {
>> -		VENDOR_EXT_KEY(XTHEADVECTOR);
>> +		if (has_xtheadvector() && has_fpu())
>
> xtheadvector is also gated on FPU=y so this is a reduntant addition. Is
> it worthwhile to make this change?

With CONFIG_FPU=y, has_fpu() is set to false when a single hart doesn't
have the D, and has_xtheadvector() could still be true.

>                                                                      Is
> it worthwhile to make this change?

I think that it's sensible to mimic the validation we do for the
non-vendor extension, but users of vendor extensions likely already have
to go out of their way to utilize them, so they can do the sanity checks
too... I can drop the last two patches in v2.

Thanks.