linux-kernel - Re: [PATCH v2] arm64/mm: Hoist synchronization out of set

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Message-ID: <ZS6EvMiJ0QF5INkv@arm.com>
Date:   Tue, 17 Oct 2023 13:57:32 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Ryan Roberts <ryan.roberts@....com>
Cc:     kernel test robot <lkp@...el.com>, Will Deacon <will@...nel.org>,
        Steven Price <steven.price@....com>,
        Peter Collingbourne <pcc@...gle.com>, llvm@...ts.linux.dev,
        oe-kbuild-all@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64/mm: Hoist synchronization out of set_ptes() loop

On Tue, Oct 17, 2023 at 08:36:43AM +0100, Ryan Roberts wrote:
> On 16/10/2023 18:54, Catalin Marinas wrote:
> > On Sat, Oct 14, 2023 at 05:15:51AM +0800, kernel test robot wrote:
> >> kernel test robot noticed the following build warnings:
> >>
> >> [auto build test WARNING on arm64/for-next/core]
> >> [also build test WARNING on arm-perf/for-next/perf arm/for-next kvmarm/next soc/for-next linus/master v6.6-rc5 next-20231013]
> >> [cannot apply to arm/fixes]
> >> [If your patch is applied to the wrong git tree, kindly drop us a note.
> >> And when submitting patch, we suggest to use '--base' as documented in
> >> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> >>
> >> url:    https://github.com/intel-lab-lkp/linux/commits/Ryan-Roberts/arm64-mm-Hoist-synchronization-out-of-set_ptes-loop/20231005-231636
> >> base:   https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
> >> patch link:    https://lore.kernel.org/r/20231005140730.2191134-1-ryan.roberts%40arm.com
> >> patch subject: [PATCH v2] arm64/mm: Hoist synchronization out of set_ptes() loop
> >> config: arm64-allyesconfig (https://download.01.org/0day-ci/archive/20231014/202310140531.BQQwt3NQ-lkp@intel.com/config)
> >> compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
> >> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231014/202310140531.BQQwt3NQ-lkp@intel.com/reproduce)
> >>
> >> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> >> the same patch/commit), kindly add following tags
> >> | Reported-by: kernel test robot <lkp@...el.com>
> >> | Closes: https://lore.kernel.org/oe-kbuild-all/202310140531.BQQwt3NQ-lkp@intel.com/
> >>
> >> All warnings (new ones prefixed by >>):
> >>
> >>    In file included from net/ipv4/route.c:66:
> >>    In file included from include/linux/mm.h:29:
> >>    In file included from include/linux/pgtable.h:6:
> >>>> arch/arm64/include/asm/pgtable.h:344:65: warning: parameter 'addr' set but not used [-Wunused-but-set-parameter]
> >>      344 | static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
> >>          |                                                                 ^
> >>    1 warning generated.
> > 
> > Thanks for the report. I think something like below will do (I'll test
> > and commit as a separate patch, it's not something that Ryan's patch
> > introduces):
> 
> I was actually just trying to repro this and was planning to send out a v3 of my
> patch. But if you are happy to handle it as you suggest, then I guess you don't
> need anything further from me?

If you feel like testing, please give this a go ;)

------------8<---------------------------
>From e6255237acfc21e92252653c3ed42446ef67f625 Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@....com>
Date: Tue, 17 Oct 2023 11:57:55 +0100
Subject: [PATCH] arm64: Mark the 'addr' argument to set_ptes() and
 __set_pte_at() as unused

This argument is not used by the arm64 implementation. Mark it as
__always_unused and also remove the unnecessary 'addr' increment in
set_ptes().

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202310140531.BQQwt3NQ-lkp@intel.com/
Cc: Will Deacon <will@...nel.org>
Cc: Ryan Roberts <ryan.roberts@....com>
---
 arch/arm64/include/asm/pgtable.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 68984ba9ce2a..b19a8aee684c 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -341,8 +341,9 @@ static inline void __sync_cache_and_tags(pte_t pte, unsigned int nr_pages)
 		mte_sync_tags(pte, nr_pages);
 }
 
-static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
-			      pte_t *ptep, pte_t pte, unsigned int nr)
+static inline void set_ptes(struct mm_struct *mm,
+			    unsigned long __always_unused addr,
+			    pte_t *ptep, pte_t pte, unsigned int nr)
 {
 	page_table_check_ptes_set(mm, ptep, pte, nr);
 	__sync_cache_and_tags(pte, nr);
@@ -353,7 +354,6 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
 		if (--nr == 0)
 			break;
 		ptep++;
-		addr += PAGE_SIZE;
 		pte_val(pte) += PAGE_SIZE;
 	}
 }
@@ -528,7 +528,8 @@ static inline pmd_t pmd_mkdevmap(pmd_t pmd)
 #define pud_pfn(pud)		((__pud_to_phys(pud) & PUD_MASK) >> PAGE_SHIFT)
 #define pfn_pud(pfn,prot)	__pud(__phys_to_pud_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot))
 
-static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
+static inline void __set_pte_at(struct mm_struct *mm,
+				unsigned long __always_unused addr,
 				pte_t *ptep, pte_t pte, unsigned int nr)
 {
 	__sync_cache_and_tags(pte, nr);