Message-ID: <aHDah15CN7Y16Lxx@yilunxu-OptiPlex-7050>
Date: Fri, 11 Jul 2025 17:33:59 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Vishal Annapurve <vannapurve@...gle.com>,
	Yan Zhao <yan.y.zhao@...el.com>, Alexey Kardashevskiy <aik@....com>,
	Fuad Tabba <tabba@...gle.com>,
	Ackerley Tng <ackerleytng@...gle.com>, kvm@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-fsdevel@...r.kernel.org, ajones@...tanamicro.com,
	akpm@...ux-foundation.org, amoorthy@...gle.com,
	anthony.yznaga@...cle.com, anup@...infault.org,
	aou@...s.berkeley.edu, bfoster@...hat.com,
	binbin.wu@...ux.intel.com, brauner@...nel.org,
	catalin.marinas@....com, chao.p.peng@...el.com,
	chenhuacai@...nel.org, dave.hansen@...el.com, david@...hat.com,
	dmatlack@...gle.com, dwmw@...zon.co.uk, erdemaktas@...gle.com,
	fan.du@...el.com, fvdl@...gle.com, graf@...zon.com,
	haibo1.xu@...el.com, hch@...radead.org, hughd@...gle.com,
	ira.weiny@...el.com, isaku.yamahata@...el.com, jack@...e.cz,
	james.morse@....com, jarkko@...nel.org, jgowans@...zon.com,
	jhubbard@...dia.com, jroedel@...e.de, jthoughton@...gle.com,
	jun.miao@...el.com, kai.huang@...el.com, keirf@...gle.com,
	kent.overstreet@...ux.dev, kirill.shutemov@...el.com,
	liam.merwick@...cle.com, maciej.wieczor-retman@...el.com,
	mail@...iej.szmigiero.name, maz@...nel.org, mic@...ikod.net,
	michael.roth@....com, mpe@...erman.id.au, muchun.song@...ux.dev,
	nikunj@....com, nsaenz@...zon.es, oliver.upton@...ux.dev,
	palmer@...belt.com, pankaj.gupta@....com, paul.walmsley@...ive.com,
	pbonzini@...hat.com, pdurrant@...zon.co.uk, peterx@...hat.com,
	pgonda@...gle.com, pvorel@...e.cz, qperret@...gle.com,
	quic_cvanscha@...cinc.com, quic_eberman@...cinc.com,
	quic_mnalajal@...cinc.com, quic_pderrin@...cinc.com,
	quic_pheragu@...cinc.com, quic_svaddagi@...cinc.com,
	quic_tsoni@...cinc.com, richard.weiyang@...il.com,
	rick.p.edgecombe@...el.com, rientjes@...gle.com,
	roypat@...zon.co.uk, rppt@...nel.org, seanjc@...gle.com,
	shuah@...nel.org, steven.price@....com, steven.sistare@...cle.com,
	suzuki.poulose@....com, thomas.lendacky@....com,
	usama.arif@...edance.com, vbabka@...e.cz, viro@...iv.linux.org.uk,
	vkuznets@...hat.com, wei.w.wang@...el.com, will@...nel.org,
	willy@...radead.org, xiaoyao.li@...el.com, yilun.xu@...el.com,
	yuzenghui@...wei.com, zhiquan1.li@...el.com
Subject: Re: [RFC PATCH v2 04/51] KVM: guest_memfd: Introduce
 KVM_GMEM_CONVERT_SHARED/PRIVATE ioctls

> > > 
> > > Only *guest permitted* conversion should change the page. I.e only when
> > > VMM is dealing with the KVM_HC_MAP_GPA_RANGE hypercall. Not sure if we
> > > could just let QEMU ensure this or KVM/guestmemfd should ensure this.
> > 
> > I think it should not be part of the kernel, no need. From a kernel
> > perspective userspace has requested a shared/private conversion and if
> > it wasn't agreed with the VM then it will explode.
> 
> I'm OK with it now. It's simple if we don't try to recover from the
> explosion. Although I see the after explosion processing in kernel is
> complex and not sure how it will advance.

I see the discussion in another thread about similar issue. That TDX
Module BUG causes S-EPT unmap impossible and just KVM_BUG_ON(). But this
conversion issue is a little different, usually it's not decent to panic
because of userspace request. So may need further error handling, or a
KVM/gmemfd kAPI to disallow/allow conversion and prevent more complex
error.

Thanks,
Yilun

> 
> Thanks,
> Yilun
> 
> > 
> > Jason
> 

Powered by blists - more mailing lists