linux-kernel - Re: [PATCH] x86/virt/tdx: Use precalculated TDVPR page physical address

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Message-ID: <033f56f9-fb66-4bf5-b25a-f2f8b964cd4e@intel.com>
Date: Mon, 20 Oct 2025 08:10:21 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, linux-kernel@...r.kernel.org,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, "Kirill A. Shutemov" <kas@...nel.org>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Kai Huang <kai.huang@...el.com>,
 Isaku Yamahata <isaku.yamahata@...el.com>,
 Vishal Annapurve <vannapurve@...gle.com>, Thomas Huth <thuth@...hat.com>,
 Adrian Hunter <adrian.hunter@...el.com>, linux-coco@...ts.linux.dev,
 kvm@...r.kernel.org, Farrah Chen <farrah.chen@...el.com>
Subject: Re: [PATCH] x86/virt/tdx: Use precalculated TDVPR page physical
 address

On 10/20/25 07:42, Sean Christopherson wrote:
>> In a perfect world, we'd have sparse annotations for the vaddr, paddr,
>> pfn, dma_addr_t and all the other address spaces. Until then, I like
>> passing struct page around.
> But that clearly doesn't work since now the raw paddr is being passed in many
> places, and we end up with goofy code like this where one param takes a raw paddr,
> and another uses page_to_phys().
> 
> @@ -1583,7 +1578,7 @@ u64 tdh_vp_addcx(struct tdx_vp *vp, struct page *tdcx_page)
>  {
>         struct tdx_module_args args = {
>                 .rcx = page_to_phys(tdcx_page),
> -               .rdx = tdx_tdvpr_pa(vp),
> +               .rdx = vp->tdvpr_pa,
>         };

I'm kinda dense normally and my coffee hasn't kicked in yet. What
clearly does not work there?

Yeah, vp->tdvpr_pa is storing a physical address as a raw u64 and not a
'struct page'. That's not ideal. But it's also for a pretty good reason.

The "use 'struct page *' instead of u64 for physical addresses" thingy
is a good pattern, not an absolute rule. Use it when you can, but
abandon it for the greater good when necessary.

I don't hate the idea of a tdx_page_t. I'm just not sure it's worth the
trouble. I'd certainly take a good look at the patches if someone hacked
it together.