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

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Message-ID: <f43286ef-3dea-4637-a34e-b9b70d2741bf@arm.com>
Date: Fri, 19 Dec 2025 12:20:13 +0000
From: Robin Murphy <robin.murphy@....com>
To: Barry Song <21cnbao@...il.com>, catalin.marinas@....com,
 m.szyprowski@...sung.com, will@...nel.org
Cc: 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 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