linux-kernel - Re: [PATCH v2 10/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX flush operations

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Message-ID: <136df713-64f1-4dfb-90c2-88c613fc72a7@intel.com>
Date: Wed, 13 Nov 2024 13:41:50 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>
Cc: "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
 "Yao, Yuan" <yuan.yao@...el.com>, "Huang, Kai" <kai.huang@...el.com>,
 "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
 "Li, Xiaoyao" <xiaoyao.li@...el.com>,
 "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "tony.lindgren@...ux.intel.com" <tony.lindgren@...ux.intel.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>,
 "Chatre, Reinette" <reinette.chatre@...el.com>,
 "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 10/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX
 flush operations

On 11/13/24 13:18, Edgecombe, Rick P wrote:
> -u64 tdh_vp_flush(u64 tdvpr)
> +u64 tdh_vp_flush(void *tdvpr)
>  {
>         struct tdx_module_args args = {
> -               .rcx = tdvpr,
> +               .rcx = __pa(tdvpr),
>         };
> 
>         return seamcall(TDH_VP_FLUSH, &args);

I'd much rather these be:

	tdx->tdvpr_page = alloc_page(GFP_KERNEL_ACCOUNT);

and then you pass around the struct page and do:

	.rcx = page_to_phys(tdvpr)

Because it's honestly _not_ an address.  It really and truly is a page
and you never need to dereference it, only pass it around as a handle.
You could get fancy and make a typedef for it or something, or even

struct tdvpr_struct {
	struct page *page;
}

But that's probably overkill.  It would help to, for instance, avoid
mixing up these two pages:

+u64 tdh_vp_create(u64 tdr, u64 tdvpr);

But it wouldn't help as much for these:

+u64 tdh_vp_addcx(u64 tdvpr, u64 tdcx);
+u64 tdh_vp_init(u64 tdvpr, u64 initial_rcx);
+u64 tdh_vp_init_apicid(u64 tdvpr, u64 initial_rcx, u32 x2apicid);
+u64 tdh_vp_flush(u64 tdvpr);
+u64 tdh_vp_rd(u64 tdvpr, u64 field, u64 *data);
+u64 tdh_vp_wr(u64 tdvpr, u64 field, u64 data, u64 mask);

Except for (for instance) 'tdr' vs. 'tdvpr' confusion.  Spot the bug:

	tdh_vp_flush(kvm_tdx(foo)->tdr_pa);
	tdh_vp_flush(kvm_tdx(foo)->tdrvp_pa);

Do you want the compiler's help for those?