Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h

Vincenzo Frascino
2020-03-16T10:29:41Z

On 3/16/20 10:26 AM, Catalin Marinas wrote:
> On Mon, Mar 16, 2020 at 10:22:15AM +0000, Mark Rutland wrote:
>> On Mon, Mar 16, 2020 at 09:42:32AM +0000, Vincenzo Frascino wrote:
>>> On 3/15/20 6:30 PM, Catalin Marinas wrote:
>>>> On Fri, Mar 13, 2020 at 03:43:37PM +0000, Vincenzo Frascino wrote:
>>>>> --- /dev/null
>>>>> +++ b/arch/arm64/include/asm/vdso/processor.h
>>>>> @@ -0,0 +1,31 @@
>>>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>>>> +/*
>>>>> + * Copyright (C) 2020 ARM Ltd.
>>>>> + */
>>>>> +#ifndef __ASM_VDSO_PROCESSOR_H
>>>>> +#define __ASM_VDSO_PROCESSOR_H
>>>>> +
>>>>> +#ifndef __ASSEMBLY__
>>>>> +
>>>>> +#include <asm/page-def.h>
>>>>> +
>>>>> +#ifdef CONFIG_COMPAT
>>>>> +#if defined(CONFIG_ARM64_64K_PAGES) && defined(CONFIG_KUSER_HELPERS)
>>>>> +/*
>>>>> + * With CONFIG_ARM64_64K_PAGES enabled, the last page is occupied
>>>>> + * by the compat vectors page.
>>>>> + */
>>>>> +#define TASK_SIZE_32 UL(0x100000000)
>>>>> +#else
>>>>> +#define TASK_SIZE_32 (UL(0x100000000) - PAGE_SIZE)
>>>>> +#endif /* CONFIG_ARM64_64K_PAGES */
>>>>> +#endif /* CONFIG_COMPAT */
>>>>
>>>> Just curious, what's TASK_SIZE_32 used for in the vDSO code? You don't
>>>> seem to move TASK_SIZE.
>>>>
>>>
>>> I tried to fine grain the headers as much as I could in order to avoid
>>> unneeded/unwanted inclusions:
>>> * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to
>>> arch/arm64/kernel/vdso32/vgettimeofday.c).
>>> * TASK_SIZE is not required by the vdso library hence it is not present in
>>> these headers.
>>
>> It would be worth noting the former point in the commit message, since
>> it can be surprising.
>>
>> I also think it's worth keeping the definitions together if that's easy,
>> as it makes it easier to navigate the codebase, even if TASK_SIZE isn't
>> necessary for the VDSO itself.
>
> It won't work as TASK_SIZE requires (on arm64) test_thread_flag() which
> can't be made available to the vDSO.
>

Ups, I did not see this :) luckily I agree ;)

--
Regards,
Vincenzo