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Date:   Sat, 13 May 2023 23:35:26 +0200
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Subject: Re: [PATCH 08/23] parisc: add pte_unmap() to balance get_ptep()
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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>,
        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>,
        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,
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        linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <77a5d8c-406b-7068-4f17-23b7ac53bc83@google.com>
 <44ebbf90-5fbb-2815-17c7-fcfe3c87d78e@google.com>
From:   Helge Deller <deller@gmx.de>
In-Reply-To: <44ebbf90-5fbb-2815-17c7-fcfe3c87d78e@google.com>
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Precedence: bulk

Hi Hugh,

On 5/10/23 06:52, Hugh Dickins wrote:
> To keep balance in future, remember to pte_unmap() after a successful
> get_ptep().  And (we might as well) pretend that flush_cache_pages()
> really needed a map there, to read the pfn before "unmapping".
>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---
>   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 1d3b8bc8a623..b0c969b3a300 100644
> --- a/arch/parisc/kernel/cache.c
> +++ b/arch/parisc/kernel/cache.c
> @@ -425,10 +425,15 @@ 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 {
>   			/*
> @@ -560,14 +565,20 @@ 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))

^^^^^
One ")" too much and lacks a trailing ";"
Should be:
		needs_flush =3D pte_needs_flush(*ptep);

With that fixed the kernel compiles and boots sucessfully on parisc.

Helge