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Date:   Mon, 19 Jun 2023 05:55:42 +0200
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Subject: Re: [PATCH v2 08/23] parisc: add pte_unmap() to balance get_ptep()
Content-Language: en-US
To:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Michal Simek <monstr@monstr.eu>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        John David Anglin <dave.anglin@bell.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Alexandre Ghiti <alexghiti@rivosinc.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        "David S. Miller" <davem@davemloft.net>,
        Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>, x86@kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
        linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <a4963be9-7aa6-350-66d0-2ba843e1af44@google.com>
 <653369-95ef-acd2-d6ea-e95f5a997493@google.com>
From:   Helge Deller <deller@gmx.de>
In-Reply-To: <653369-95ef-acd2-d6ea-e95f5a997493@google.com>
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Precedence: bulk

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@google.com>

For the parisc parts:

Acked-by: Helge Deller <deller@gmx.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 =3D (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
>   		addr =3D mpnt->vm_start + offset;
>   		if (parisc_requires_coherency()) {
> +			bool needs_flush =3D false;
>   			pte_t *ptep;
>
>   			ptep =3D get_ptep(mpnt->vm_mm, addr);
> -			if (ptep && pte_needs_flush(*ptep))
> +			if (ptep) {
> +				needs_flush =3D 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 =3D get_ptep(vma->vm_mm, vmaddr);
> +	bool needs_flush =3D 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 =3D get_ptep(vma->vm_mm, vmaddr);
> +	if (ptep) {
> +		needs_flush =3D 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_struc=
t *vma, unsigned long start, u
>   	pte_t *ptep;
>
>   	for (addr =3D start; addr < end; addr +=3D PAGE_SIZE) {
> +		bool needs_flush =3D 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 =3D get_ptep(vma->vm_mm, addr);
> -		if (ptep && pte_needs_flush(*ptep)) {
> +		if (ptep) {
> +			needs_flush =3D pte_needs_flush(*ptep);
> +			pfn =3D pte_pfn(*ptep);
> +			pte_unmap(ptep);
> +		}
> +		if (needs_flush) {
>   			if (parisc_requires_coherency()) {
>   				flush_user_cache_page(vma, addr);
>   			} else {
> -				pfn =3D pte_pfn(*ptep);
>   				if (WARN_ON(!pfn_valid(pfn)))
>   					return;
>   				__flush_cache_page(vma, addr, PFN_PHYS(pfn));