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

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Message-ID: <037e52a151c4af1ed4b417eeff5df4e5de853c0c.camel@intel.com>
Date: Wed, 13 Nov 2024 21:48:21 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>
CC: "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>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "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 Wed, 2024-11-13 at 13:41 -0800, Dave Hansen wrote:
> 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.

That is a really good point.

> 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?

Haha, we have already had bugs around these names actually. If we we end up with
the current arch/x86 based approach we can see if we can fit it in.