From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5F71135A3AD; Fri, 1 May 2026 19:01:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777662074; cv=none; b=nnXGwfmziNrorTVJpKabSfHFgtDziA6EaA3n0TRNquAtfhWk4jU1dIlfutjvTPpep1MVg0QRYYM63tc12+9PC0ZmvJvw1YNfA8uDMOaNpgKkr2QyxGAha3ycWx7BIdRgRImk5SVaSVoOSMYDC6LHBFBlSTfhTIX/7ybzJFyQrlw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777662074; c=relaxed/simple; bh=bGN+GuXKLt8BkjsU+fTyN3JEqVQmZxPi1LhFItNPdDc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=a5/TII8v0a5vGoKXRniLRmzbwaIJJsV5nrin9cFsWzZeMLEVaa0J3ViAauL9Mzy8bzgo5s40WvFU0GMH82L6/wcdkumw1X7lPXN/2n4ippW02YG1lxG3xuNWuPtkpRvVrrwcVYd/tvUvuoa6YLzUyUyqTR+hBxT0mXTwYA+4qM8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EYMuspBM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EYMuspBM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 39200C2BCB4; Fri, 1 May 2026 19:01:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777662074; bh=bGN+GuXKLt8BkjsU+fTyN3JEqVQmZxPi1LhFItNPdDc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=EYMuspBM5/RFx2O2cUQIAmnFfT8rY+UfcrOAaqxbDyIsmHDOfYzOpSURXYENSWldi fSXRA8CGtzePoDQJnzHOEhIHRY8llLl17U8+32V5YZz+xyNq3Z4oRn3aifz0Q6VDFq BziQhEiooZPEGX7WDaZNmduLow6vAD+vYFPwIpgYT+Wdw8qKSi56scx9NIwzS+molL zrwnRnK+RXlTKOWWGBMU9AmUZI8sXYlq+TvKDjgHXtMuLwEJ1JgzC08ViIlADDBxCC ZJ6lRJy9fGOsAerc8zYDvbY1FucwCBzv9mI5v9IJKdWPTPkFqPjKkhm4QYZeNUtdBf ensB43tRLW6Ag== Message-ID: <109bc59e-1308-4505-b8c6-3376aed74585@kernel.org> Date: Fri, 1 May 2026 21:01:09 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_vma_mapped_walk: add missing pgtable entry accessors To: Alexander Gordeev Cc: Andrew Morton , Lorenzo Stoakes , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260427052000.196402-1-agordeev@linux.ibm.com> <69c4c12c-7cdc-4a17-9eb7-6fb1a61f9834@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/29/26 15:47, Alexander Gordeev wrote: > On Mon, Apr 27, 2026 at 11:02:50AM +0200, David Hildenbrand (Arm) wrote: >> On 4/27/26 07:20, Alexander Gordeev wrote: >>> Convert pgtable direct entry dereferences to the corresponding >>> pXdp_get() accessors. Use ptep_get_lockless() variant for PTE >>> reads when no lock is taken. >>> >>> Signed-off-by: Alexander Gordeev >>> --- >>> mm/page_vma_mapped.c | 12 ++++++------ >>> 1 file changed, 6 insertions(+), 6 deletions(-) >>> >>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >>> index b38a1d00c971..a4520bb10d2a 100644 >>> --- a/mm/page_vma_mapped.c >>> +++ b/mm/page_vma_mapped.c >>> @@ -41,7 +41,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp, >>> if (!pvmw->pte) >>> return false; >>> >>> - ptent = ptep_get(pvmw->pte); >>> + ptent = ptep_get_lockless(pvmw->pte); > > (*) > >>> if (pte_none(ptent)) { >>> return false; >>> @@ -219,17 +219,17 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) >>> restart: >>> do { >>> pgd = pgd_offset(mm, pvmw->address); >>> - if (!pgd_present(*pgd)) { >>> + if (!pgd_present(pgdp_get(pgd))) { >>> step_forward(pvmw, PGDIR_SIZE); >>> continue; >>> } >>> p4d = p4d_offset(pgd, pvmw->address); >>> - if (!p4d_present(*p4d)) { >>> + if (!p4d_present(p4dp_get(p4d))) { >>> step_forward(pvmw, P4D_SIZE); >>> continue; >>> } >>> pud = pud_offset(p4d, pvmw->address); >>> - if (!pud_present(*pud)) { >>> + if (!pud_present(pudp_get(pud))) { >>> step_forward(pvmw, PUD_SIZE); >>> continue; >> >> Wasn't there a problem with folded page tables, where we would no longer be able >> to optimize out the folded page table accesses? > > Ok, that is a different topic. I actually tried to resolve the lockless > issue(s) in (*) while the direct dereferences just seemed to be relevant > to go along (similarly to the GUP patch). > > But I would rather resend ptep_get() => ptep_get_lockless() fixes for > this patch. > > Would it work? You mean only sending {*) ? -- Cheers, David