linux-kernel - Re: [PATCHv2 00/12] TDX: Enable Dynamic PAMT

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Message-ID: <4be5db34-aadb-49e3-9a94-49d39c8bd31d@intel.com>
Date: Tue, 9 Sep 2025 08:23:42 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Kiryl Shutsemau <kirill@...temov.name>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 pbonzini@...hat.com, seanjc@...gle.com, dave.hansen@...ux.intel.com,
 rick.p.edgecombe@...el.com, isaku.yamahata@...el.com, kai.huang@...el.com,
 yan.y.zhao@...el.com, chao.gao@...el.com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, kvm@...r.kernel.org, x86@...nel.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 00/12] TDX: Enable Dynamic PAMT

On 9/9/25 04:16, Kiryl Shutsemau wrote:
> Dynamic PAMT pages are stored into PAMT_2M entry and you cannot have 2M
> page and have Dynamic 4K entries stored there at the same time.

That sounds like a TDX module implementation bug to me.

Worst possible case, the TDX module could double the
'sysinfo_tdmr->pamt_2m_entry_size' and use the other half for more pointers.

> And it is going to be very wasteful. With huge pages, in most cases, you
> only need dynamic PAMT for control pages. You will have a lot of memory
> sitting in stash with zero use.

I think it's going to be hard to convince me without actual data on this
one.

Even then, we're talking about 0.4% of system memory. So how much code
and complexity are we talking about in order to save a *maximum* of 0.4%
of system memory?