linux-kernel - Re: [PATCH v2 00/19] mm: Support huge pfnmaps

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: <20240828234958.GE3773488@nvidia.com>
Date: Wed, 28 Aug 2024 20:49:58 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Jiaqi Yan <jiaqiyan@...gle.com>
Cc: Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Gavin Shan <gshan@...hat.com>,
	Catalin Marinas <catalin.marinas@....com>, x86@...nel.org,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alistair Popple <apopple@...dia.com>, kvm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Sean Christopherson <seanjc@...gle.com>,
	Oscar Salvador <osalvador@...e.de>, Borislav Petkov <bp@...en8.de>,
	Zi Yan <ziy@...dia.com>, Axel Rasmussen <axelrasmussen@...gle.com>,
	David Hildenbrand <david@...hat.com>,
	Yan Zhao <yan.y.zhao@...el.com>, Will Deacon <will@...nel.org>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH v2 00/19] mm: Support huge pfnmaps

On Wed, Aug 28, 2024 at 09:10:34AM -0700, Jiaqi Yan wrote:
> On Wed, Aug 28, 2024 at 7:24 AM Jason Gunthorpe <jgg@...dia.com> wrote:
> >
> > On Tue, Aug 27, 2024 at 05:42:21PM -0700, Jiaqi Yan wrote:
> >
> > > Instead of removing the whole pud, can driver or memory_failure do
> > > something similar to non-struct-page-version of split_huge_page? So
> > > driver doesn't need to re-fault good pages back?
> >
> > It would be far nicer if we didn't have to poke a hole in a 1G mapping
> > just for memory failure reporting.
> 
> If I follow this, which of the following sounds better? 1. remove pud
> and rely on the driver to re-fault PFNs that it knows are not poisoned
> (what Peter suggested), or 2. keep the pud and allow access to both
> good and bad PFNs.

In practice I think people will need 2, as breaking up a 1G mapping
just because a few bits are bad will destroy the VM performance.

For this the expectation would be for the VM to co-operate and not
keep causing memory failures, or perhaps for the platform to spare in
good memory somehow.

> Or provide some knob (configured by ?) so that kernel + driver can
> switch between the two?

This is also sounding reasonable, especially if we need some
alternative protocol to signal userspace about the failed memory
besides fault and SIGBUS.

Jason