linux-kernel - Re: [PATCH v6 01/21] x86/tdx: Use enum to define page level of TDX supported page sizes

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Message-ID: <20221027135134.ya62y6lg2kh4yujb@box.shutemov.name>
Date:   Thu, 27 Oct 2022 16:51:34 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v6 01/21] x86/tdx: Use enum to define page level of TDX
 supported page sizes

On Thu, Oct 27, 2022 at 08:42:16AM +0000, Huang, Kai wrote:
> On Thu, 2022-10-27 at 15:08 +0800, Li, Xiaoyao wrote:
> > > @@ -663,27 +662,16 @@ static bool try_accept_one(phys_addr_t *start,
> > > unsigned long len,
> > >    	if (len < accept_size)
> > >    		return false;
> > >    
> > > +	/* TDX only supports 4K/2M/1G page sizes */
> > 
> > yes, a page can be mapped as 1G size to TD via secure/shared EPT. But 
> > for this particular TDX_ACCEPT_PAGE case, it only supports 4K and 2M 
> > currently, which is defined in TDX module spec.
> 
> I checked the TDX module public spec, and it appears you are right.  But I am
> not sure whether it will be changed in the future?

The spec says:

	Level of the Secure EPT entry that maps the private page to be
	accepted: either 0 (4KB) or 1 (2MB) – see 20.5.1

Yes, it is about 4k and 2M, but it also refers 20.5.1, which lists sizes
up to 16PB.

Ultimately, it does not matter: if TDX module doesn't support the size or
cannot accept the memory for other reason guest kernel will fallback to
smaller size.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov