linux-kernel - Re: [RFC PATCH 03/21] x86/virt/tdx: Add SEAMCALL wrapper tdh_mem_page

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Message-ID: <aCahn+rpeighJP2J@yzhao56-desk.sh.intel.com>
Date: Fri, 16 May 2025 10:23:27 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Li, Xiaoyao"
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Subject: Re: [RFC PATCH 03/21] x86/virt/tdx: Add SEAMCALL wrapper
 tdh_mem_page_demote()

On Fri, May 16, 2025 at 01:28:52AM +0800, Edgecombe, Rick P wrote:
> On Thu, 2025-05-15 at 16:26 +0800, Yan Zhao wrote:
> > On Wed, May 14, 2025 at 02:19:56AM +0800, Edgecombe, Rick P wrote:
> > > On Thu, 2025-04-24 at 11:04 +0800, Yan Zhao wrote:
> > > > From: Xiaoyao Li <xiaoyao.li@...el.com>
> > > > 
> > > > Add a wrapper tdh_mem_page_demote() to invoke SEAMCALL TDH_MEM_PAGE_DEMOTE
> > > > to demote a huge leaf entry to a non-leaf entry in S-EPT. Currently, the
> > > > TDX module only supports demotion of a 2M huge leaf entry. After a
> > > > successful demotion, the old 2M huge leaf entry in S-EPT is replaced with a
> > > > non-leaf entry, linking to the newly-added page table page. The newly
> > > > linked page table page then contains 512 leaf entries, pointing to the 2M
> > > > guest private pages.
> > > > 
> > > > The "gpa" and "level" direct the TDX module to search and find the old
> > > > huge leaf entry.
> > > > 
> > > > As the new non-leaf entry points to a page table page, callers need to
> > > > pass in the page table page in parameter "page".
> > > > 
> > > > In case of S-EPT walk failure, the entry, level and state where the error
> > > > was detected are returned in ext_err1 and ext_err2.
> > > > 
> > > > On interrupt pending, SEAMCALL TDH_MEM_PAGE_DEMOTE returns error
> > > > TDX_INTERRUPTED_RESTARTABLE.
> > > > 
> > > > [Yan: Rebased and split patch, wrote changelog]
> > > 
> > > We should add the level of detail here like we did for the base series ones.
> > I'll provide changelog details under "---" of each patch in the next version.
> 
> I mean the commit log (above the "---") needs the same tip style treatment as
> the other SEAMCALL wrapper patches.
I thought I have followed the style.
Sorry that if you think the commit msg is too simple without showing details
of this SEAMCALL. I can provide a detailed on in the next version if that's the
concern you mentioned above.

> >  
> > > > 
> > > > Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> > > > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > > > Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> > > > ---
> > > >  arch/x86/include/asm/tdx.h  |  2 ++
> > > >  arch/x86/virt/vmx/tdx/tdx.c | 20 ++++++++++++++++++++
> > > >  arch/x86/virt/vmx/tdx/tdx.h |  1 +
> > > >  3 files changed, 23 insertions(+)
> > > > 
> > > > diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> > > > index 26ffc792e673..08eff4b2f5e7 100644
> > > > --- a/arch/x86/include/asm/tdx.h
> > > > +++ b/arch/x86/include/asm/tdx.h
> > > > @@ -177,6 +177,8 @@ u64 tdh_mng_key_config(struct tdx_td *td);
> > > >  u64 tdh_mng_create(struct tdx_td *td, u16 hkid);
> > > >  u64 tdh_vp_create(struct tdx_td *td, struct tdx_vp *vp);
> > > >  u64 tdh_mng_rd(struct tdx_td *td, u64 field, u64 *data);
> > > > +u64 tdh_mem_page_demote(struct tdx_td *td, u64 gpa, int level, struct page *page,
> > > > +			u64 *ext_err1, u64 *ext_err2);
> > > >  u64 tdh_mr_extend(struct tdx_td *td, u64 gpa, u64 *ext_err1, u64 *ext_err2);
> > > >  u64 tdh_mr_finalize(struct tdx_td *td);
> > > >  u64 tdh_vp_flush(struct tdx_vp *vp);
> > > > diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> > > > index a66d501b5677..5699dfe500d9 100644
> > > > --- a/arch/x86/virt/vmx/tdx/tdx.c
> > > > +++ b/arch/x86/virt/vmx/tdx/tdx.c
> > > > @@ -1684,6 +1684,26 @@ u64 tdh_mng_rd(struct tdx_td *td, u64 field, u64 *data)
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(tdh_mng_rd);
> > > >  
> > > > +u64 tdh_mem_page_demote(struct tdx_td *td, u64 gpa, int level, struct page *page,
> > > > +			u64 *ext_err1, u64 *ext_err2)
> > > > +{
> > > > +	struct tdx_module_args args = {
> > > > +		.rcx = gpa | level,
> > > 
> > > This will only ever be level 2MB, how about dropping the arg?
> > Do you mean hardcoding level to be 2MB in tdh_mem_page_demote()?
> 
> Yea, we don't support 1GB, so the level arg on the wrapper is superfluous.
I'm not sure. It's not like tdh_mem_page_add() where the TDX module just only
supports 4KB.

But your point that permitting 1GB in tdh_mem_page_demote() in x86 code until
after KVM TDX code adds 1GB support also makes sense.

> > The SEAMCALL TDH_MEM_PAGE_DEMOTE supports level of 1GB in current TDX module.
> > 
> > > > +		.rdx = tdx_tdr_pa(td),
> > > > +		.r8 = page_to_phys(page),
> > > > +	};
> > > > +	u64 ret;
> > > > +
> > > > +	tdx_clflush_page(page);
> > > > +	ret = seamcall_ret(TDH_MEM_PAGE_DEMOTE, &args);
> > > > +
> > > > +	*ext_err1 = args.rcx;
> > > > +	*ext_err2 = args.rdx;