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

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Message-ID: <aQsBI1/SIXGbf9nA@yzhao56-desk.sh.intel.com>
Date: Wed, 5 Nov 2025 15:47:47 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, 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 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.
> 
> 
> [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/