Message-ID: <f4f2a0297e38ac45e4438342ac2c882b91544acb.camel@intel.com>
Date: Fri, 23 Jan 2026 00:01:09 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "ackerleytng@...gle.com" <ackerleytng@...gle.com>, "Annapurve, Vishal"
	<vannapurve@...gle.com>
CC: "david@...nel.org" <david@...nel.org>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "catalin.marinas@....com" <catalin.marinas@....com>,
	"svens@...ux.ibm.com" <svens@...ux.ibm.com>, "jgross@...e.com"
	<jgross@...e.com>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"surenb@...gle.com" <surenb@...gle.com>, "vbabka@...e.cz" <vbabka@...e.cz>,
	"riel@...riel.com" <riel@...riel.com>, "pfalcato@...e.de" <pfalcato@...e.de>,
	"x86@...nel.org" <x86@...nel.org>, "rppt@...nel.org" <rppt@...nel.org>,
	"thuth@...hat.com" <thuth@...hat.com>, "borntraeger@...ux.ibm.com"
	<borntraeger@...ux.ibm.com>, "maz@...nel.org" <maz@...nel.org>,
	"palmer@...belt.com" <palmer@...belt.com>, "ast@...nel.org" <ast@...nel.org>,
	"peterx@...hat.com" <peterx@...hat.com>, "alex@...ti.fr" <alex@...ti.fr>,
	"pjw@...nel.org" <pjw@...nel.org>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "tglx@...utronix.de" <tglx@...utronix.de>,
	"hca@...ux.ibm.com" <hca@...ux.ibm.com>, "willy@...radead.org"
	<willy@...radead.org>, "wyihan@...gle.com" <wyihan@...gle.com>,
	"ryan.roberts@....com" <ryan.roberts@....com>, "jolsa@...nel.org"
	<jolsa@...nel.org>, "yang@...amperecomputing.com"
	<yang@...amperecomputing.com>, "jmattson@...gle.com" <jmattson@...gle.com>,
	"aneesh.kumar@...nel.org" <aneesh.kumar@...nel.org>, "luto@...nel.org"
	<luto@...nel.org>, "haoluo@...gle.com" <haoluo@...gle.com>,
	"patrick.roy@...ux.dev" <patrick.roy@...ux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "coxu@...hat.com"
	<coxu@...hat.com>, "mhocko@...e.com" <mhocko@...e.com>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
	"mlevitsk@...hat.com" <mlevitsk@...hat.com>, "jgg@...pe.ca" <jgg@...pe.ca>,
	"loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>, "song@...nel.org"
	<song@...nel.org>, "oupton@...nel.org" <oupton@...nel.org>,
	"Liam.Howlett@...cle.com" <Liam.Howlett@...cle.com>, "kernel@...0n.name"
	<kernel@...0n.name>, "Jonathan.Cameron@...wei.com"
	<Jonathan.Cameron@...wei.com>, "lorenzo.stoakes@...cle.com"
	<lorenzo.stoakes@...cle.com>, "jhubbard@...dia.com" <jhubbard@...dia.com>,
	"jthoughton@...gle.com" <jthoughton@...gle.com>, "martin.lau@...ux.dev"
	<martin.lau@...ux.dev>, "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
	"peterz@...radead.org" <peterz@...radead.org>, "kvmarm@...ts.linux.dev"
	<kvmarm@...ts.linux.dev>, "eddyz87@...il.com" <eddyz87@...il.com>,
	"hpa@...or.com" <hpa@...or.com>, "yonghong.song@...ux.dev"
	<yonghong.song@...ux.dev>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, "shuah@...nel.org" <shuah@...nel.org>,
	"chenhuacai@...nel.org" <chenhuacai@...nel.org>, "prsampat@....com"
	<prsampat@....com>, "kevin.brodsky@....com" <kevin.brodsky@....com>,
	"maobibo@...ngson.cn" <maobibo@...ngson.cn>, "shijie@...amperecomputing.com"
	<shijie@...amperecomputing.com>, "suzuki.poulose@....com"
	<suzuki.poulose@....com>, "itazur@...zon.co.uk" <itazur@...zon.co.uk>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "yuzenghui@...wei.com"
	<yuzenghui@...wei.com>, "gor@...ux.ibm.com" <gor@...ux.ibm.com>,
	"dev.jain@....com" <dev.jain@....com>, "daniel@...earbox.net"
	<daniel@...earbox.net>, "jackabt@...zon.co.uk" <jackabt@...zon.co.uk>,
	"agordeev@...ux.ibm.com" <agordeev@...ux.ibm.com>, "andrii@...nel.org"
	<andrii@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>,
	"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
	"aou@...s.berkeley.edu" <aou@...s.berkeley.edu>, "joey.gouly@....com"
	<joey.gouly@....com>, "derekmn@...zon.com" <derekmn@...zon.com>,
	"xmarcalx@...zon.co.uk" <xmarcalx@...zon.co.uk>, "linux-s390@...r.kernel.org"
	<linux-s390@...r.kernel.org>, "kpsingh@...nel.org" <kpsingh@...nel.org>,
	"kalyazin@...zon.co.uk" <kalyazin@...zon.co.uk>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "sdf@...ichev.me" <sdf@...ichev.me>,
	"jackmanb@...gle.com" <jackmanb@...gle.com>, "bp@...en8.de" <bp@...en8.de>,
	"corbet@....net" <corbet@....net>, "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>, "jannh@...gle.com" <jannh@...gle.com>,
	"john.fastabend@...il.com" <john.fastabend@...il.com>, "kas@...nel.org"
	<kas@...nel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"will@...nel.org" <will@...nel.org>, "seanjc@...gle.com" <seanjc@...gle.com>
Subject: Re: [PATCH v9 07/13] KVM: guest_memfd: Add flag to remove from direct
 map

On Thu, 2026-01-22 at 14:47 -0800, Ackerley Tng wrote:
> 
> There's no use case I can think of for unmapping TDX private memory
> from the host direct map, but Sean's suggestion
> https://lore.kernel.org/all/aWpcDrGVLrZOqdcg@google.com/ won't even
> let shared guest_memfd memory be unmapped from the direct map for TDX
> VMs.

Ah!

> 
> Actually, does TDX's clflush that assumes presence in the direct map
> apply only for private pages, or all pages?
> 
> If TDX's clflush only happens for private pages, then we could
> restore private pages to the direct map, and then we'd be safe even
> for TDX?

Yes, just private pages need the special treatment. But it will be much
simpler to start with just blocking the option for TDX. A shared pages
only mode could come later.

In general I think we should try to break things up like this when we
can. Kernel code is not set in stone, only ABI. I think it will lead to
overall faster upstreaming, because the series' can be simpler.

Powered by blists - more mailing lists