linux-kernel - Re: [RFC v1 1/4] kho: Introduce KHO page table data structures

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: <20250917163200.GC1391379@nvidia.com>
Date: Wed, 17 Sep 2025 13:32:00 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Jason Miu <jasonmiu@...gle.com>, Alexander Graf <graf@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Changyuan Lyu <changyuanl@...gle.com>,
	David Matlack <dmatlack@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Joel Granados <joel.granados@...nel.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Mike Rapoport <rppt@...nel.org>, Petr Mladek <pmladek@...e.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Steven Chen <chenste@...ux.microsoft.com>,
	Yan Zhao <yan.y.zhao@...el.com>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC v1 1/4] kho: Introduce KHO page table data structures

On Wed, Sep 17, 2025 at 12:18:39PM -0400, Pasha Tatashin wrote:
> On Wed, Sep 17, 2025 at 8:22 AM Jason Gunthorpe <jgg@...dia.com> wrote:
> >
> > On Tue, Sep 16, 2025 at 07:50:16PM -0700, Jason Miu wrote:
> > > + * kho_order_table
> > > + * +-------------------------------+--------------------+
> > > + * | 0 order| 1 order| 2 order ... | HUGETLB_PAGE_ORDER |
> > > + * ++------------------------------+--------------------+
> > > + *  |
> > > + *  |
> > > + *  v
> > > + * ++------+
> > > + * |  Lv6  | kho_page_table
> > > + * ++------+
> >
> > I seem to remember suggesting this could be simplified without the
> > special case 7h level table table for order.
> >
> > Encode the phys address as:
> >
> > (order << 51) | (phys >> (PAGE_SHIFT + order))
> 
> Why 51 and not 52, this limits to 63bit address space, is it not?

Yeah, might have got the math off

> I like the idea, but I'm trying to find the benefits compared to the
> current per-order tree approach.

It is probably about half the code compared to what I see here because
everything is agressively simplified.

> 3. It slightly complicates the logic in the new kernel. Instead of
> simply iterating a known tree for a specific order, the boot-time
> walker would need to reconstruct the per-order subtrees, and walk
> them.

The core walker just runs over a range, it is easy to compute the
range.

Jason