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

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Message-ID: <aQr9jW/7zwWJaDFf@yzhao56-desk.sh.intel.com>
Date: Wed, 5 Nov 2025 15:32:29 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.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 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].

@@ -853,6 +859,10 @@ 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_class_and_subclass(&inode->i_mapping->invalidate_lock,
+                                              &inode->i_sb->s_type->invalidate_lock_key, 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/