linux-kernel - Re: [PATCH 1/6] arm64: Provide dcache_by_myline_op

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Message-ID: <CAGsJ_4wRcz7NFw2PiBCb54gmJwTt7=UG1fn2UEJ9_gR687Y4Uw@mail.gmail.com>
Date: Sun, 21 Dec 2025 15:22:03 +0800
From: Barry Song <21cnbao@...il.com>
To: Robin Murphy <robin.murphy@....com>
Cc: catalin.marinas@....com, m.szyprowski@...sung.com, will@...nel.org, 
	ada.coupriediaz@....com, anshuman.khandual@....com, ardb@...nel.org, 
	iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, maz@...nel.org, ryan.roberts@....com, 
	surenb@...gle.com, v-songbaohua@...o.com, zhengtangquan@...o.com
Subject: Re: [PATCH 1/6] arm64: Provide dcache_by_myline_op_nosync helper

On Fri, Dec 19, 2025 at 8:20 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2025-12-19 5:36 am, Barry Song wrote:
> > From: Barry Song <v-songbaohua@...o.com>
> >
> > dcache_by_myline_op ensures completion of the data cache operations for a
> > region, while dcache_by_myline_op_nosync only issues them without waiting.
> > This enables deferred synchronization so completion for multiple regions
> > can be handled together later.
>
> This is a super-low-level internal macro with only two users... Frankly I'd
> just do as below.
>
> Thanks,
> Robin.
>
> ----->8-----
>
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index f0ca7196f6fa..26e983c331c5 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -367,18 +367,17 @@ alternative_endif
>         .endm
>
>   /*
> - * Macro to perform a data cache maintenance for the interval
> - * [start, end) with dcache line size explicitly provided.
> + * Main loop for a data cache maintenance operation. Caller to provide the
> + * dcache line size and take care of relevant synchronisation afterwards.
>    *
>    *    op:             operation passed to dc instruction
> - *     domain:         domain used in dsb instruction
>    *    start:          starting virtual address of the region
>    *    end:            end virtual address of the region
>    *    linesz:         dcache line size
>    *    fixup:          optional label to branch to on user fault
>    *    Corrupts:       start, end, tmp
>    */
> -       .macro dcache_by_myline_op op, domain, start, end, linesz, tmp, fixup
> +       .macro raw_dcache_by_line_op op, start, end, linesz, tmp, fixup
>         sub     \tmp, \linesz, #1
>         bic     \start, \start, \tmp
>   .Ldcache_op\@:
> @@ -402,7 +401,6 @@ alternative_endif
>         add     \start, \start, \linesz
>         cmp     \start, \end
>         b.lo    .Ldcache_op\@
> -       dsb     \domain
>
>         _cond_uaccess_extable .Ldcache_op\@, \fixup
>         .endm
> @@ -420,7 +418,8 @@ alternative_endif
>    */
>         .macro dcache_by_line_op op, domain, start, end, tmp1, tmp2, fixup
>         dcache_line_size \tmp1, \tmp2
> -       dcache_by_myline_op \op, \domain, \start, \end, \tmp1, \tmp2, \fixup
> +       raw_dcache_by_line_op \op, \start, \end, \tmp1, \tmp2, \fixup
> +       dsb \domain
>         .endm
>
>   /*
> diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S
> index 413f899e4ac6..efdb6884058e 100644
> --- a/arch/arm64/kernel/relocate_kernel.S
> +++ b/arch/arm64/kernel/relocate_kernel.S
> @@ -64,7 +64,8 @@ SYM_CODE_START(arm64_relocate_new_kernel)
>         mov     x19, x13
>         copy_page x13, x12, x1, x2, x3, x4, x5, x6, x7, x8
>         add     x1, x19, #PAGE_SIZE
> -       dcache_by_myline_op civac, sy, x19, x1, x15, x20
> +       raw_dcache_by_line_op civac, x19, x1, x15, x20
> +       dsb     sy
>         b       .Lnext
>   .Ltest_indirection:
>         tbz     x16, IND_INDIRECTION_BIT, .Ltest_destination
>

Thanks, Robin.  Really much better!
dcache_by_line_op_nosync could be:

/*
 * Macro to perform a data cache maintenance for the interval
 * [start, end) without waiting for completion
 *
 *      op:             operation passed to dc instruction
 *      start:          starting virtual address of the region
 *      end:            end virtual address of the region
 *      fixup:          optional label to branch to on user fault
 *      Corrupts:       start, end, tmp1, tmp2
 */
        .macro dcache_by_line_op_nosync op, start, end, tmp1, tmp2, fixup
        dcache_line_size \tmp1, \tmp2
        raw_dcache_by_myline_op \op, \start, \end, \tmp1, \tmp2, \fixup
        .endm

Thanks
Barry