linux-kernel - Re: [PATCH v2 08/23] parisc: add pte_unmap() to balance get

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Date:   Mon, 19 Jun 2023 05:55:42 +0200
From:   Helge Deller <deller@....de>
To:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        John David Anglin <dave.anglin@...l.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Alexandre Ghiti <alexghiti@...osinc.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "David S. Miller" <davem@...emloft.net>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 08/23] parisc: add pte_unmap() to balance get_ptep()

On 6/8/23 21:18, Hugh Dickins wrote:
> To keep balance in future, remember to pte_unmap() after a successful
> get_ptep().  And act as if flush_cache_pages() really needs a map there,
> to read the pfn before "unmapping", to be sure page table is not removed.
>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>

For the parisc parts:

Acked-by: Helge Deller <deller@....de> # parisc

Helge


> ---
>   arch/parisc/kernel/cache.c | 26 +++++++++++++++++++++-----
>   1 file changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
> index ca4a302d4365..501160250bb7 100644
> --- a/arch/parisc/kernel/cache.c
> +++ b/arch/parisc/kernel/cache.c
> @@ -426,10 +426,15 @@ void flush_dcache_page(struct page *page)
>   		offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
>   		addr = mpnt->vm_start + offset;
>   		if (parisc_requires_coherency()) {
> +			bool needs_flush = false;
>   			pte_t *ptep;
>
>   			ptep = get_ptep(mpnt->vm_mm, addr);
> -			if (ptep && pte_needs_flush(*ptep))
> +			if (ptep) {
> +				needs_flush = pte_needs_flush(*ptep);
> +				pte_unmap(ptep);
> +			}
> +			if (needs_flush)
>   				flush_user_cache_page(mpnt, addr);
>   		} else {
>   			/*
> @@ -561,14 +566,20 @@ EXPORT_SYMBOL(flush_kernel_dcache_page_addr);
>   static void flush_cache_page_if_present(struct vm_area_struct *vma,
>   	unsigned long vmaddr, unsigned long pfn)
>   {
> -	pte_t *ptep = get_ptep(vma->vm_mm, vmaddr);
> +	bool needs_flush = false;
> +	pte_t *ptep;
>
>   	/*
>   	 * The pte check is racy and sometimes the flush will trigger
>   	 * a non-access TLB miss. Hopefully, the page has already been
>   	 * flushed.
>   	 */
> -	if (ptep && pte_needs_flush(*ptep))
> +	ptep = get_ptep(vma->vm_mm, vmaddr);
> +	if (ptep) {
> +		needs_flush = pte_needs_flush(*ptep);
> +		pte_unmap(ptep);
> +	}
> +	if (needs_flush)
>   		flush_cache_page(vma, vmaddr, pfn);
>   }
>
> @@ -635,17 +646,22 @@ static void flush_cache_pages(struct vm_area_struct *vma, unsigned long start, u
>   	pte_t *ptep;
>
>   	for (addr = start; addr < end; addr += PAGE_SIZE) {
> +		bool needs_flush = false;
>   		/*
>   		 * The vma can contain pages that aren't present. Although
>   		 * the pte search is expensive, we need the pte to find the
>   		 * page pfn and to check whether the page should be flushed.
>   		 */
>   		ptep = get_ptep(vma->vm_mm, addr);
> -		if (ptep && pte_needs_flush(*ptep)) {
> +		if (ptep) {
> +			needs_flush = pte_needs_flush(*ptep);
> +			pfn = pte_pfn(*ptep);
> +			pte_unmap(ptep);
> +		}
> +		if (needs_flush) {
>   			if (parisc_requires_coherency()) {
>   				flush_user_cache_page(vma, addr);
>   			} else {
> -				pfn = pte_pfn(*ptep);
>   				if (WARN_ON(!pfn_valid(pfn)))
>   					return;
>   				__flush_cache_page(vma, addr, PFN_PHYS(pfn));