On 3/19/25 09:04, Anshuman Khandual wrote: > On 3/19/25 07:16, Yury Norov wrote: >> + Catalin Marinas, ARM maillist >> >> Hi Catalin and everyone, > > Hello Yury, > >> >> Anshuman Khandual asked me to merge GENMASK_U128() saying it's >> important for ARM to stabilize API. While it's a dead code, I >> accepted his patch as he promised to add users shortly. >> >> Now it's more than half a year since that. There's no users, >> and no feedback from Anshuman. > > My apologies to have missed your email earlier. Please find response > for the earlier email below as well. > >> >> Can you please tell if you still need the macro? I don't want to >> undercut your development, but if you don't need 128-bit genmasks >> there's no reason to have a dead code in the uapi. > > The code base specifically using GENMASK_U128() has not been posted > upstream (probably in next couple of months or so) till now, except > the following patch which has been not been merged and still under > review and development. > > https://lore.kernel.org/lkml/20240801054436.612024-1-anshuman.khandual@xxxxxxx/ > >> >> Thanks, >> Yury >> >> On Wed, Mar 05, 2025 at 10:22:47AM -0500, Yury Norov wrote: >>> + Anshuman Khandual <anshuman.khandual@xxxxxxx> >>> >>> Anshuman, >>> >>> I merged your GENMASK_U128() because you said it's important for your >>> projects, and that it will get used in the kernel soon. >>> >>> Now it's in the kernel for more than 6 month, but no users were added. >>> Can you clarify if you still need it, and if so why it's not used? > > We would need it but although the code using GENMASK_U128() has not been > posted upstream. > >>> >>> As you see, people add another fixed-types GENMASK() macros, and their >>> implementation differ from GENMASK_U128(). > > I will take a look. Is GENMASK_U128() being problematic for the this new > scheme ? > >>> >>> My second concern is that __GENMASK_U128() is declared in uapi, while >>> the general understanding for other fixed-type genmasks is that they >>> are not exported to users. Do you need this macro to be exported to >>> userspace? Can you show how and where it is used there? > > No, not atleast right now. > > These were moved into uapi subsequently via the following commit. > > 21a3a3d015aee ("tools headers: Synchronize {uapi/}linux/bits.h with the kernel sources") > > But in general GENMASK_U128() is needed for generating 128 bit page table > entries, related flags and masks whether in kernel or in user space for > writing kernel test cases etc. In the commit 947697c6f0f7 ("uapi: Define GENMASK_U128"), GENMASK_U128() gets defined using __GENMASK_U128() which in turn calls __BIT128() - both of which are defined in UAPI headers inside (include/uapi/linux/). Just wondering - are you suggesting to move these helpers from include/uapi/linux/ to include/linux/bits.h instead ? > >>> >>> Thanks, >>> Yury >>> >>> >>> On Wed, Mar 05, 2025 at 10:00:15PM +0900, Vincent Mailhol via B4 Relay wrote: >>>> From: Yury Norov <yury.norov@xxxxxxxxx> >>>> >>>> Add __GENMASK_t() which generalizes __GENMASK() to support different >>>> types, and implement fixed-types versions of GENMASK() based on it. >>>> The fixed-type version allows more strict checks to the min/max values >>>> accepted, which is useful for defining registers like implemented by >>>> i915 and xe drivers with their REG_GENMASK*() macros. >>>> >>>> The strict checks rely on shift-count-overflow compiler check to fail >>>> the build if a number outside of the range allowed is passed. >>>> Example: >>>> >>>> #define FOO_MASK GENMASK_U32(33, 4) >>>> >>>> will generate a warning like: >>>> >>>> ../include/linux/bits.h:41:31: error: left shift count >= width of type [-Werror=shift-count-overflow] >>>> 41 | (((t)~0ULL - ((t)(1) << (l)) + 1) & \ >>>> | ^~ >>>> >>>> Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx> >>>> Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx> >>>> Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx> >>>> Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> >>>> --- >>>> Changelog: >>>> >>>> v3 -> v4: >>>> >>>> - The v3 is one year old. Meanwhile people started using >>>> __GENMASK() directly. So instead of generalizing __GENMASK() to >>>> support different types, add a new GENMASK_t(). >>>> >>>> - replace ~0ULL by ~_ULL(0). Otherwise, __GENMASK_t() would fail >>>> in asm code. >>>> >>>> - Make GENMASK_U8() and GENMASK_U16() return an unsigned int. In >>>> v3, due to the integer promotion rules, these were returning a >>>> signed integer. By casting these to unsigned int, at least the >>>> signedness is kept. >>>> --- >>>> include/linux/bitops.h | 1 - >>>> include/linux/bits.h | 33 +++++++++++++++++++++++++++++---- >>>> 2 files changed, 29 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/include/linux/bitops.h b/include/linux/bitops.h >>>> index c1cb53cf2f0f8662ed3e324578f74330e63f935d..9be2d50da09a417966b3d11c84092bb2f4cd0bef 100644 >>>> --- a/include/linux/bitops.h >>>> +++ b/include/linux/bitops.h >>>> @@ -8,7 +8,6 @@ >>>> >>>> #include <uapi/linux/kernel.h> >>>> >>>> -#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) >>>> #define BITS_TO_LONGS(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(long)) >>>> #define BITS_TO_U64(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u64)) >>>> #define BITS_TO_U32(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u32)) >>>> diff --git a/include/linux/bits.h b/include/linux/bits.h >>>> index 5f68980a1b98d771426872c74d7b5c0f79e5e802..f202e46d2f4b7899c16d975120f3fa3ae41556ae 100644 >>>> --- a/include/linux/bits.h >>>> +++ b/include/linux/bits.h >>>> @@ -12,6 +12,7 @@ >>>> #define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG)) >>>> #define BIT_ULL_WORD(nr) ((nr) / BITS_PER_LONG_LONG) >>>> #define BITS_PER_BYTE 8 >>>> +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) >>>> >>>> /* >>>> * Create a contiguous bitmask starting at bit position @l and ending at >>>> @@ -25,14 +26,38 @@ >>>> >>>> #define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(const_true((l) > (h))) >>>> >>>> -#define GENMASK(h, l) \ >>>> - (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) >>>> -#define GENMASK_ULL(h, l) \ >>>> - (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l)) >>>> +/* >>>> + * Generate a mask for the specified type @t. Additional checks are made to >>>> + * guarantee the value returned fits in that type, relying on >>>> + * shift-count-overflow compiler check to detect incompatible arguments. >>>> + * For example, all these create build errors or warnings: >>>> + * >>>> + * - GENMASK(15, 20): wrong argument order >>>> + * - GENMASK(72, 15): doesn't fit unsigned long >>>> + * - GENMASK_U32(33, 15): doesn't fit in a u32 >>>> + */ >>>> +#define GENMASK_t(t, h, l) \ >>>> + (GENMASK_INPUT_CHECK(h, l) + \ >>>> + (((t)~ULL(0) - ((t)1 << (l)) + 1) & \ >>>> + ((t)~ULL(0) >> (BITS_PER_TYPE(t) - 1 - (h))))) >>>> + >>>> +#define GENMASK(h, l) GENMASK_t(unsigned long, h, l) >>>> +#define GENMASK_ULL(h, l) GENMASK_t(unsigned long long, h, l) >>>> >>>> /* >>>> * Missing asm support >>>> * >>>> + * __GENMASK_U*() depends on BITS_PER_TYPE() which would not work in the asm >>>> + * code as BITS_PER_TYPE() relies on sizeof(), something not available in >>>> + * asm. Nethertheless, the concept of fixed width integers is a C thing which >>>> + * does not apply to assembly code. >>>> + */ >>>> +#define GENMASK_U8(h, l) ((unsigned int)GENMASK_t(u8, h, l)) >>>> +#define GENMASK_U16(h, l) ((unsigned int)GENMASK_t(u16, h, l)) >>>> +#define GENMASK_U32(h, l) GENMASK_t(u32, h, l) >>>> +#define GENMASK_U64(h, l) GENMASK_t(u64, h, l) >>>> + >>>> +/* >>>> * __GENMASK_U128() depends on _BIT128() which would not work >>>> * in the asm code, as it shifts an 'unsigned __int128' data >>>> * type instead of direct representation of 128 bit constants >>>> >>>> -- >>>> 2.45.3 >>>> >
