linux-kernel - Re: [RFC PATCH v1 07/37] KVM: Introduce KVM_SET_MEMORY

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: <aPpEPZ4YfrRHIkal@google.com>
Date: Thu, 23 Oct 2025 08:05:33 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Ackerley Tng <ackerleytng@...gle.com>
Cc: Steven Price <steven.price@....com>, cgroups@...r.kernel.org, kvm@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org, x86@...nel.org, 
	akpm@...ux-foundation.org, binbin.wu@...ux.intel.com, bp@...en8.de, 
	brauner@...nel.org, chao.p.peng@...el.com, chenhuacai@...nel.org, 
	corbet@....net, dave.hansen@...el.com, dave.hansen@...ux.intel.com, 
	david@...hat.com, dmatlack@...gle.com, erdemaktas@...gle.com, 
	fan.du@...el.com, fvdl@...gle.com, haibo1.xu@...el.com, hannes@...xchg.org, 
	hch@...radead.org, hpa@...or.com, hughd@...gle.com, ira.weiny@...el.com, 
	isaku.yamahata@...el.com, jack@...e.cz, james.morse@....com, 
	jarkko@...nel.org, jgg@...pe.ca, jgowans@...zon.com, jhubbard@...dia.com, 
	jthoughton@...gle.com, jun.miao@...el.com, kai.huang@...el.com, 
	keirf@...gle.com, kent.overstreet@...ux.dev, liam.merwick@...cle.com, 
	maciej.wieczor-retman@...el.com, mail@...iej.szmigiero.name, 
	maobibo@...ngson.cn, mathieu.desnoyers@...icios.com, maz@...nel.org, 
	mhiramat@...nel.org, mhocko@...nel.org, mic@...ikod.net, michael.roth@....com, 
	mingo@...hat.com, mlevitsk@...hat.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, peterx@...hat.com, 
	pgonda@...gle.com, prsampat@....com, pvorel@...e.cz, qperret@...gle.com, 
	richard.weiyang@...il.com, rick.p.edgecombe@...el.com, rientjes@...gle.com, 
	rostedt@...dmis.org, roypat@...zon.co.uk, rppt@...nel.org, 
	shakeel.butt@...ux.dev, shuah@...nel.org, suzuki.poulose@....com, 
	tabba@...gle.com, tglx@...utronix.de, thomas.lendacky@....com, 
	vannapurve@...gle.com, vbabka@...e.cz, viro@...iv.linux.org.uk, 
	vkuznets@...hat.com, will@...nel.org, willy@...radead.org, wyihan@...gle.com, 
	xiaoyao.li@...el.com, yan.y.zhao@...el.com, yilun.xu@...el.com, 
	yuzenghui@...wei.com
Subject: Re: [RFC PATCH v1 07/37] KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2

On Thu, Oct 23, 2025, Ackerley Tng wrote:
> Sean Christopherson <seanjc@...gle.com> writes:
> 
> > On Wed, Oct 22, 2025, Ackerley Tng wrote:
> >> Ackerley Tng <ackerleytng@...gle.com> writes:
> >> 
> >> Found another issue with KVM_CAP_MEMORY_ATTRIBUTES2.
> >> 
> >> KVM_CAP_MEMORY_ATTRIBUTES2 was defined to do the same thing as
> >> KVM_CAP_MEMORY_ATTRIBUTES, but that's wrong since
> >> KVM_CAP_MEMORY_ATTRIBUTES2 should indicate the presence of
> >> KVM_SET_MEMORY_ATTRIBUTES2 and struct kvm_memory_attributes2.
> >
> > No?  If no attributes are supported, whether or not KVM_SET_MEMORY_ATTRIBUTES2
> > exists is largely irrelevant.
> 
> That's true.
> 
> > We can even provide the same -ENOTTY errno by
> > checking that _any_ attributes are supported, i.e. so that doing
> > KVM_SET_MEMORY_ATTRIBUTES2 on KVM without any support whatsoever fails in the
> > same way that KVM with code support but no attributes fails.
> 
> IIUC KVM_SET_MEMORY_ATTRIBUTES doesn't fail with -ENOTTY now when there
> are no valid attributes.
> 
> Even if there's no valid attributes (as in
> kvm_supported_mem_attributes() returns 0), it's possible to call
> KVM_SET_MEMORY_ATTRIBUTES with .attributes set to 0, which will be a
> no-op, but will return 0.
> 
> I think this is kind of correct behavior since .attributes = 0 is
> actually a valid expression for "I want this range to be shared", and
> for a VM that doesn't support private memory, it's a valid expression.
> 
> 
> The other way that there are "no attributes" would be if there are no
> /VM/ attributes, in which case KVM_SET_MEMORY_ATTRIBUTES, sent to as a
> vm ioctl, will return -ENOTTY.

Ya, this is what I was trying to say with "_any_ attributes are supported".  I.e.
by "any" I meant "any attributes in KVM for VMs vs. gmems", not "any attributes
for this specific VM/gmem instance".

> > In other words, I don't see why it can't do both.  Even if we can't massage the
> > right errno, I would much rather KVM_SET_MEMORY_ATTRIBUTES2 enumerate the set of
> 
> Did you mean KVM_CAP_MEMORY_ATTRIBUTES2 in the line above?

Doh, yes.