linux-kernel - Re: [PATCH v4 07/16] x86/virt/tdx: Add tdx_alloc/free

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: <730de4be289ed7e3550d40170ea7d67e5d37458f.camel@intel.com>
Date: Mon, 1 Dec 2025 22:39:09 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "Huang, Kai" <kai.huang@...el.com>, "Li,
 Xiaoyao" <xiaoyao.li@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>, "Wu, Binbin" <binbin.wu@...el.com>,
	"kas@...nel.org" <kas@...nel.org>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"mingo@...hat.com" <mingo@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "tglx@...utronix.de" <tglx@...utronix.de>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "nik.borisov@...e.com"
	<nik.borisov@...e.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "Gao, Chao"
	<chao.gao@...el.com>, "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org"
	<x86@...nel.org>
Subject: Re: [PATCH v4 07/16] x86/virt/tdx: Add tdx_alloc/free_page() helpers

On Thu, 2025-11-27 at 18:11 +0200, Nikolay Borisov wrote:
> > +/* Number PAMT pages to be provided to TDX module per 2M region of PA */
> > +static int tdx_dpamt_entry_pages(void)
> > +{
> > +	if (!tdx_supports_dynamic_pamt(&tdx_sysinfo))
> > +		return 0;
> > +
> > +	return tdx_sysinfo.tdmr.pamt_4k_entry_size * PTRS_PER_PTE /
> > PAGE_SIZE;
> > +}
> 
> Isn't this guaranteed to return 2 always as per the ABI? Can't the 
> allocation of the 2 pages be moved closer to where it's used - in 
> tdh_phymem_pamt_add which will simplify things a bit?

Yea, it could be simpler if it was always guaranteed to be 2 pages. But it was
my understanding that it would not be a fixed size. Can you point to what docs
makes you think that?

Another option would be to ask TDX folks to make it fixed, and then require an
opt-in for it to be expanded later if needed. I would have to check on them on
the reasoning for it being dynamic sized. I'm not sure if it is *that*
complicated at this point though. Once there is more than one, the loops becomes
tempting. And if we loop over 2 we could easily loop over n.