linux-kernel - Re: [PATCH v3 04/25] KVM: x86/mmu: Add dedicated API to map guest

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] [day] [month] [year] [list]

Message-ID: <aQtsqXPaZo2SMdJU@google.com>
Date: Wed, 5 Nov 2025 07:26:33 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>, 
	Huacai Chen <chenhuacai@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>, 
	Anup Patel <anup@...infault.org>, Paul Walmsley <pjw@...nel.org>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, 
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	"Kirill A. Shutemov" <kas@...nel.org>, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org, loongarch@...ts.linux.dev, 
	linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, 
	kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org, 
	x86@...nel.org, linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Ira Weiny <ira.weiny@...el.com>, Kai Huang <kai.huang@...el.com>, 
	Michael Roth <michael.roth@....com>, Vishal Annapurve <vannapurve@...gle.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Ackerley Tng <ackerleytng@...gle.com>, 
	Binbin Wu <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v3 04/25] KVM: x86/mmu: Add dedicated API to map
 guest_memfd pfn into TDP MMU

On Wed, Nov 05, 2025, Yan Zhao wrote:
> On Wed, Nov 05, 2025 at 03:32:29PM +0800, Yan Zhao wrote:
> > On Tue, Nov 04, 2025 at 09:57:26AM -0800, Sean Christopherson wrote:
> > > On Thu, Oct 30, 2025, Yan Zhao wrote:
> > > > On Wed, Oct 22, 2025 at 12:53:53PM +0800, Yan Zhao wrote:
> > > > > On Thu, Oct 16, 2025 at 05:32:22PM -0700, Sean Christopherson wrote:
> > > > > > Link: https://lore.kernel.org/all/20250709232103.zwmufocd3l7sqk7y@amd.com
> > > > > 
> > > > > Hi Sean,                                                                         
> > > > > 
> > > > > Will you post [1] to fix the AB-BA deadlock issue for huge page in-place
> > > > > conversion as well?
> > > 
> > > If you (or anyone) has the bandwidth, please pick it up.  I won't have cycles to
> > > look at that for many weeks (potentially not even this calendar year).
> > Got it!
> > On the other hand, do you think we can address the warning as below?
> > The code is based on [2].
> Hmm, updated the diff.
> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 7b4a4474d468..543e1eb9db65 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -853,6 +853,9 @@ static int kvm_gmem_init_inode(struct inode *inode, loff_t size, u64 flags)
>         inode->i_size = size;
>         mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
>         mapping_set_inaccessible(inode->i_mapping);
> +       if (flags &GUEST_MEMFD_FLAG_MMAP)
> +               lockdep_set_subclass(&inode->i_mapping->invalidate_lock, 1);
> +
>         /* Unmovable mappings are supposed to be marked unevictable as well. */
>         WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
> 
>  
> > As noted in [3], the only scenario can trigger the warning after [2] is when a
> > process creates a TDX VM with non-in-place-conversion guest_memfd and a normal
> > VM with in-place-conversion guest_memfd. The two invalidate_lock's don't contend
> > with each other theoretically.

Hmm, no, I think we need to hoist gup() call outside of filemap_invalidate_lock(),
because I don't think this is strictly limited to TDX VMs without in-place
conversion.  Even with in-place conversion, I think KVM should allow the source
page to be shared memory, at which point I believe this becomes a legimate AB-BA
issue.

In general, playing lockdep games with so many subsystems involved terrifies me.

> > [2] https://lore.kernel.org/all/cover.1760731772.git.ackerleytng@google.com/
> > [3] https://lore.kernel.org/all/aQMi%2Fn9DVyeaWsVH@yzhao56-desk.sh.intel.com/