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b=vKsenpAgWw4PdXzyPEvRPTtM55CEkmIuOB06QpIL1HFkJaREveyrGwluU/V2fuGGi q5TX7S4AkHAZd7NNOwoSKw4Q9atEptf5m3QREyryBOZ6qV8TyjDyjvN90WleZ6Id1/ W86zK2v0N2lj5WYbHcSmtpC+EsAstPuLctnj85O0= Date: Thu, 9 Oct 2025 18:15:59 -0700 From: Andrew Morton To: Samuel Holland Cc: Palmer Dabbelt , Paul Walmsley , linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Conor Dooley , Alexandre Ghiti , Emil Renner Berthing , Rob Herring , Krzysztof Kozlowski Subject: Re: [PATCH v2 00/18] riscv: Memory type control for platforms with physical memory aliases Message-Id: <20251009181559.7bfa3dce6cb7265822b2d5c5@linux-foundation.org> In-Reply-To: <20251009015839.3460231-1-samuel.holland@sifive.com> References: <20251009015839.3460231-1-samuel.holland@sifive.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 3079E1A000E X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: hpenysm64h6t6xyeigqgs681na56my4c X-HE-Tag: 1760058962-728215 X-HE-Meta: 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 0FIHSx0/ Jp7ACUVA8timojQjsUhWYihW7OcQSovFwUgWRIMXCn/l33V9TmMMp37ekgh625EmQbM+T6MB0Dolq81TKBZIlrf9hKljVGR8qyD4sLC6rMQR/fekmvWhYnPsEblphWC8vXb7wR3mLqlTK+NoL+2b3OtQMdgiYqsbR2Qy968Udq8AY+E/mhj067sQn6fNLWeazUl9Rb0RBGp/FSf1zsVfJ7WcigSofYx0TiFf7HWDxu6djYjiHYwajH0ZI5KFGEV9aqgtBtb0tIb7JCk8j58mNxSY9Odi2H6512CpNKhxWcup5ycfxXUMeTApq/UNJf3DxF69UxKM7qSXb8ftwL7LUb3sf8G+XL+7YHQZAYsGH5lTABxP+3aRqTrVqf4sxZaGKAvjT X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 8 Oct 2025 18:57:36 -0700 Samuel Holland wrote: > On some RISC-V platforms, including StarFive JH7100 and ESWIN EIC7700, > DRAM is mapped to multiple physical address ranges, with each alias > having a different set of statically-determined Physical Memory > Attributes (PMAs), such as cacheability. Software can alter the PMAs for > a page by selecting a PFN from the corresponding physical address range. > On these platforms, this is the only way to allocate noncached memory > for use with noncoherent DMA. Well that's weird. > --- a/mm/ptdump.c > +++ b/mm/ptdump.c > @@ -31,7 +31,7 @@ static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr, > unsigned long next, struct mm_walk *walk) > { > struct ptdump_state *st = walk->private; > - pgd_t val = READ_ONCE(*pgd); > + pgd_t val = pgdp_get(pgd); > > #if CONFIG_PGTABLE_LEVELS > 4 && \ > (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) OK, but how are we to maintain this? Will someone be running grep/coccinelle/whatever on each kernel release? Please give some thought to finding a way to break the build if someone uses a plain dereference or a READ_ONCE(). Or add a checkpatch rule. Or something. Let's not rely upon the whole world knowing about this.