linux-kernel - Re: [PATCH 10/19] KVM: Use follow

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: <CAJHvVchObsUVW2QFroA8pexyXUgKR178knLoaEacMTL6iLoHNQ@mail.gmail.com>
Date: Mon, 12 Aug 2024 15:47:29 -0700
From: Axel Rasmussen <axelrasmussen@...gle.com>
To: Peter Xu <peterx@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Sean Christopherson <seanjc@...gle.com>, Oscar Salvador <osalvador@...e.de>, Jason Gunthorpe <jgg@...dia.com>, 
	linux-arm-kernel@...ts.infradead.org, x86@...nel.org, 
	Will Deacon <will@...nel.org>, Gavin Shan <gshan@...hat.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Zi Yan <ziy@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Catalin Marinas <catalin.marinas@....com>, Ingo Molnar <mingo@...hat.com>, 
	Alistair Popple <apopple@...dia.com>, Borislav Petkov <bp@...en8.de>, David Hildenbrand <david@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, kvm@...r.kernel.org, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Alex Williamson <alex.williamson@...hat.com>, 
	Yan Zhao <yan.y.zhao@...el.com>
Subject: Re: [PATCH 10/19] KVM: Use follow_pfnmap API

On Mon, Aug 12, 2024 at 11:58 AM Peter Xu <peterx@...hat.com> wrote:
>
> On Fri, Aug 09, 2024 at 10:23:20AM -0700, Axel Rasmussen wrote:
> > On Fri, Aug 9, 2024 at 9:09 AM Peter Xu <peterx@...hat.com> wrote:
> > >
> > > Use the new pfnmap API to allow huge MMIO mappings for VMs.  The rest work
> > > is done perfectly on the other side (host_pfn_mapping_level()).
> >
> > I don't think it has to be done in this series, but a future
> > optimization to consider is having follow_pfnmap just tell the caller
> > about the mapping level directly. It already found this information as
> > part of its walk. I think there's a possibility to simplify KVM /
> > avoid it having to do its own walk again later.
>
> AFAIU pfnmap isn't special in this case, as we do the "walk pgtable twice"
> idea also to a generic page here, so probably not directly relevant to this
> patch alone.
>
> But I agree with you, sounds like something we can consider trying.  I
> would be curious on whether the perf difference would be measurable in this
> specific case, though.  I mean, this first walk will heat up all the
> things, so I'd expect the 2nd walk (which is lockless) later be pretty fast
> normally.

Agreed, the main benefit is probably just code simplification.

>
> Thanks,
>
> --
> Peter Xu
>