linux-kernel - Re: [PATCH v2 08/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX page cache management

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Message-ID: <32f7cd5fde98acc1b9e55ab2d4616de83173adc9.camel@intel.com>
Date: Thu, 14 Nov 2024 00:32:58 +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>, "Huang,
 Kai" <kai.huang@...el.com>
CC: "Yao, Yuan" <yuan.yao@...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>,
	"sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: Re: [PATCH v2 08/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX page
 cache management

On Thu, 2024-11-14 at 13:21 +1300, Huang, Kai wrote:
> 
> On 14/11/2024 11:00 am, Edgecombe, Rick P wrote:
> > On Wed, 2024-11-13 at 13:50 -0800, Dave Hansen wrote:
> > > On 11/13/24 13:44, Edgecombe, Rick P wrote:
> > > > Moving them to arch/x86 means we need to translate some things between KVM's
> > > > parlance and the rest of the kernels. This is extra wrapping. Another example
> > > > that was used in the old SEAMCALL wrappers was gpa_t, which KVM uses to refers
> > > > to a guest physical address. void * to the host direct map doesn't fit, so we
> > > > are back to u64 or a new gpa struct (like in the other thread) to speak to the
> > > > arch/x86 layers.
> > > 
> > > I have zero issues with non-core x86 code doing a #include
> > > <linux/kvm_types.h>.  Why not just use the KVM types?
> > 
> > You know...I assumed it wouldn't work because of some internal headers. But yea.
> > Nevermind, we can just do that. Probably because the old code also referred to
> > struct kvm_tdx, it just got fully separated. Kai did you attempt this path at
> > all?
> 
> 'struct kvm_tdx' is a KVM internal structure so we cannot use that in 
> SEAMCALL wrappers in the x86 core.
> 
Yea, makes sense.

>   If you are talking about just use 
> KVM types like 'gfn_t/hpa_t' etc (by including <linux/kvm_types.h>) 
> perhaps this is fine.
> 
> But I didn't try to do in this way.  We can try if that's better, but I 
> suppose we should get Sean/Paolo's feedback here?

There are certainly a lot of style considerations here. I'm thinking to post
like an RFC. Like a fork to look at Dave's suggestions.