linux-kernel - Re: [PATCH v4] io: add io

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aUVje_QZvJ9rjedp@google.com>
Date: Fri, 19 Dec 2025 14:38:51 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Miguel Ojeda <ojeda@...nel.org>, Will Deacon <will@...nel.org>, 
	Daniel Almeida <daniel.almeida@...labora.com>, 
	Boris Brezillon <boris.brezillon@...labora.com>, Robin Murphy <robin.murphy@....com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Joerg Roedel <joro@...tes.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Asahi Lina <lina+kernel@...hilina.net>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, iommu@...ts.linux.dev, linux-mm@...ck.org
Subject: Re: [PATCH v4] io: add io_pgtable abstraction

On Fri, Dec 19, 2025 at 10:05:57AM -0400, Jason Gunthorpe wrote:
> On Fri, Dec 19, 2025 at 10:50:52AM +0000, Alice Ryhl wrote:
> > +// For now, we do not provide the ability to flush the TLB via the built-in callback mechanism.
> > +// Instead, the `map_pages` function requires the caller to explicitly flush the TLB before the
> > +// pgtable is used to access the newly created range.
> > +//
> > +// This is done because the initial user of this abstraction may perform many calls to `map_pages`
> > +// in a single batched operation, and wishes to only flush the TLB once after performing the entire
> > +// batch of mappings. These callbacks would flush too often for that use-case.
> > +//
> > +// Support for flushing the TLB in these callbacks may be added in the future.
> > +static NOOP_FLUSH_OPS: bindings::iommu_flush_ops = bindings::iommu_flush_ops {
> > +    tlb_flush_all: Some(rust_tlb_flush_all_noop),
> > +    tlb_flush_walk: Some(rust_tlb_flush_walk_noop),
> > +    tlb_add_page: None,
> > +};
> 
> This comment seems quite off..
> 
> Usually you don't flush on map, you flush on unmap. The TLB should be
> empty upon mapping and not need flushing - except for the rarer
> special cases of clearing the walk cache which cannot be detected any
> other way than using these callbacks. Doing a big flush on map to deal
> with the walk cache would be worse than implementing these callbacks.
> 
> The flush on unmap, at least for ARM style invalidations, needs these
> callbacks because they provide required information. If the actual HW
> does not use an ARM style invalidation system then this page table
> code is not optimal for it.

You should not assume that the way I worded something implies that the
GPU hardware does something weird. It's more likely that I just got
something wrong.

It looks like panthor / tyr flush the range that was modified after both
map and unmap operations.

Alice