linux-kernel - Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using VMA flags

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: <20250407161540.GG1557073@nvidia.com>
Date: Mon, 7 Apr 2025 13:15:40 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>, Ankit Agrawal <ankita@...dia.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	"joey.gouly@....com" <joey.gouly@....com>,
	"suzuki.poulose@....com" <suzuki.poulose@....com>,
	"yuzenghui@...wei.com" <yuzenghui@...wei.com>,
	"will@...nel.org" <will@...nel.org>,
	"ryan.roberts@....com" <ryan.roberts@....com>,
	"shahuang@...hat.com" <shahuang@...hat.com>,
	"lpieralisi@...nel.org" <lpieralisi@...nel.org>,
	"david@...hat.com" <david@...hat.com>,
	Aniket Agashe <aniketa@...dia.com>, Neo Jia <cjia@...dia.com>,
	Kirti Wankhede <kwankhede@...dia.com>,
	"Tarun Gupta (SW-GPU)" <targupta@...dia.com>,
	Vikram Sethi <vsethi@...dia.com>, Andy Currid <acurrid@...dia.com>,
	Alistair Popple <apopple@...dia.com>,
	John Hubbard <jhubbard@...dia.com>, Dan Williams <danw@...dia.com>,
	Zhi Wang <zhiw@...dia.com>, Matt Ochs <mochs@...dia.com>,
	Uday Dhoke <udhoke@...dia.com>, Dheeraj Nigam <dnigam@...dia.com>,
	Krishnakant Jaju <kjaju@...dia.com>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"sebastianene@...gle.com" <sebastianene@...gle.com>,
	"coltonlewis@...gle.com" <coltonlewis@...gle.com>,
	"kevin.tian@...el.com" <kevin.tian@...el.com>,
	"yi.l.liu@...el.com" <yi.l.liu@...el.com>,
	"ardb@...nel.org" <ardb@...nel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"gshan@...hat.com" <gshan@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"ddutile@...hat.com" <ddutile@...hat.com>,
	"tabba@...gle.com" <tabba@...gle.com>,
	"qperret@...gle.com" <qperret@...gle.com>,
	"kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using
 VMA flags

On Mon, Apr 07, 2025 at 08:20:09AM -0700, Sean Christopherson wrote:
> On Mon, Mar 31, 2025, Jason Gunthorpe wrote:
> > On Wed, Mar 26, 2025 at 11:24:32AM -0700, Sean Christopherson wrote:
> > > > I don't know how you reconcile the lack of host mapping and cache
> > > > maintenance. The latter cannot take place without the former.
> > > 
> > > I assume cache maintenance only requires _a_ mapping to the physical memory.
> > > With guest_memfd, KVM has the pfn (which happens to always be struct page memory
> > > today), and so can establish a VA=>PA mapping as needed.
> > 
> > This is why we are forcing FWB in this work, because we don't have a
> > VA mapping and KVM doesn't have the code to create one on demand.
> 
> I don't follow.  As it exists today, guest_memfd doesn't touch the direct map,
> i.e. there's already a kernel mapping, KVM doesn't need to create one.

This is not about guest_memfd..

When ARM KVM copies a PTE from a VMA's PTE into the S2 it may find
that the physical address does not have a struct page, in which case
it assumes the worst that it is not in the kmap and cannot be cache
flushed.

Jason