linux-kernel - Re: [PATCH] mm: add PTE pointer parameter to flush_tlb_fix_spurious

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Message-ID: <ZAYdpLCxicptr4MJ@arm.com>
Date:   Mon, 6 Mar 2023 17:06:44 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-mips <linux-mips@...r.kernel.org>,
        linux-power <linuxppc-dev@...ts.ozlabs.org>,
        linux-x86 <x86@...nel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: add PTE pointer parameter to
 flush_tlb_fix_spurious_fault()

On Mon, Mar 06, 2023 at 05:15:48PM +0100, Gerald Schaefer wrote:
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index b6ba466e2e8a..0bd18de9fd97 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -57,7 +57,7 @@ static inline bool arch_thp_swp_supported(void)
>   * fault on one CPU which has been handled concurrently by another CPU
>   * does not need to perform additional invalidation.
>   */
> -#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
> +#define flush_tlb_fix_spurious_fault(vma, address, ptep) do { } while (0)

For arm64:

Acked-by: Catalin Marinas <catalin.marinas@....com>

> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index 2c70b4d1263d..c1f6b46ec555 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -1239,7 +1239,8 @@ static inline int pte_allow_rdp(pte_t old, pte_t new)
>  }
>  
>  static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma,
> -						unsigned long address)
> +						unsigned long address,
> +						pte_t *ptep)
>  {
>  	/*
>  	 * RDP might not have propagated the PTE protection reset to all CPUs,
> @@ -1247,11 +1248,12 @@ static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma,
>  	 * NOTE: This will also be called when a racing pagetable update on
>  	 * another thread already installed the correct PTE. Both cases cannot
>  	 * really be distinguished.
> -	 * Therefore, only do the local TLB flush when RDP can be used, to avoid
> -	 * unnecessary overhead.
> +	 * Therefore, only do the local TLB flush when RDP can be used, and the
> +	 * PTE does not have _PAGE_PROTECT set, to avoid unnecessary overhead.
> +	 * A local RDP can be used to do the flush.
>  	 */
> -	if (MACHINE_HAS_RDP)
> -		asm volatile("ptlb" : : : "memory");
> +	if (MACHINE_HAS_RDP && !(pte_val(*ptep) & _PAGE_PROTECT))
> +		__ptep_rdp(address, ptep, 0, 0, 1);

I wonder whether passing the actual entry is somewhat quicker as it
avoids another memory access (though it might already be in the cache).

-- 
Catalin