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Date: Wed, 5 Feb 2025 23:17:18 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: David Hildenbrand <david@redhat.com>, Asahi Lina <lina@asahilina.net>,
	Miguel Ojeda <ojeda@kernel.org>,
	Alex Gaynor <alex.gaynor@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
	=?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
	Benno Lossin <benno.lossin@proton.me>,
	Andreas Hindborg <a.hindborg@kernel.org>,
	Alice Ryhl <aliceryhl@google.com>, Trevor Gross <tmgross@umich.edu>,
	Jann Horn <jannh@google.com>, Paolo Bonzini <pbonzini@redhat.com>,
	Danilo Krummrich <dakr@kernel.org>,
	Wedson Almeida Filho <wedsonaf@gmail.com>,
	Valentin Obst <kernel@valentinobst.de>,
	Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
	airlied@redhat.com, Abdiel Janulgue <abdiel.janulgue@gmail.com>,
	rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
	asahi@lists.linux.dev
Subject: Re: [PATCH 0/6] rust: page: Support borrowing `struct page` and
 physaddr conversion
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In-Reply-To: <20250204204947.GM2296753@ziepe.ca>

On Tue, Feb 04, 2025 at 04:49:47PM -0400, Jason Gunthorpe wrote:
> The phys_to_virt() I mean is on the page table pages themselves, not
> on a leaf.
> 
> All page table pages came from alloc_pages_node() and you'd do
> virt_to_phys() to stick them into a next-table PTE, then
> phys_to_virt() to bring them back:
> 
>   phys_to_virt(virt_to_phys(page_address(alloc_pages_node())))
> 
> Effectively.

except for s390 & ppc where the page table can be smaller than
PAGE_SIZE, so you really only have a physical address that can be
converted to a virtual address.