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Message-ID: <aLVih+zi8gW5zrJY@yzhao56-desk.sh.intel.com>
Date: Mon, 1 Sep 2025 17:08:23 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>,
<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>, <x86@...nel.org>,
<rick.p.edgecombe@...el.com>, <dave.hansen@...el.com>, <kas@...nel.org>,
<tabba@...gle.com>, <ackerleytng@...gle.com>, <quic_eberman@...cinc.com>,
<michael.roth@....com>, <david@...hat.com>, <vannapurve@...gle.com>,
<vbabka@...e.cz>, <thomas.lendacky@....com>, <pgonda@...gle.com>,
<zhiquan1.li@...el.com>, <fan.du@...el.com>, <jun.miao@...el.com>,
<ira.weiny@...el.com>, <isaku.yamahata@...el.com>, <xiaoyao.li@...el.com>,
<chao.p.peng@...el.com>
Subject: Re: [RFC PATCH v2 02/23] x86/virt/tdx: Add SEAMCALL wrapper
tdh_mem_page_demote()
On Mon, Sep 01, 2025 at 04:55:30PM +0800, Binbin Wu wrote:
>
>
> On 8/7/2025 5:41 PM, Yan Zhao wrote:
> > From: Xiaoyao Li <xiaoyao.li@...el.com>
> >
> > Introduce SEAMCALL wrapper tdh_mem_page_demote() to invoke the SEAMCALL
> > TDH_MEM_PAGE_DEMOTE, which demotes a huge leaf entry to a non-leaf entry
> > in the S-EPT.
> >
> > SEAMCALL TDH_MEM_PAGE_DEMOTE supports the demotion of 2MB or 1GB huge leaf
> > entries.
> >
> > The "gpa" and "level" parameters enable the SEAMCALL TDH_MEM_PAGE_DEMOTE to
> > walk the S-EPT for the huge leaf entry that needs to be demoted.
> >
> > The "page" parameter specifies a 4KB page that will be used in the demotion
> > operation to be added as a page table page in the S-EPT.
> >
> > Invoke tdx_clflush_page() on the 4KB page being added as a page table page.
> > This function performs CLFLUSH operations on certain TDX-capable platforms,
> > or conservatively on all TDX-capable platforms, to prevent dirty cache
> > lines from writing back later and corrupting TD memory.
> >
> > tdh_mem_page_demote() may fail. Callers can check function return value and
> > retrieve extended error info from the function output parameters "ext_err1"
> > and "ext_err2". e.g., due to S-EPT walk error or arriving interrupts.
> >
> > The TDX module has many internal locks. To avoid staying in SEAM mode for
> > too long, SEAMCALLs return a BUSY error code to the kernel instead of
> > spinning on the locks. Depending on the specific SEAMCALL, the caller may
> > need to handle this error in specific ways (e.g., retry). Therefore, return
> > the SEAMCALL error code directly to the caller without attempting to handle
> > it in the core kernel.
> >
> > Do not handle TDX_INTERRUPTED_RESTARTABLE because SEAMCALL
> > TDH_MEM_PAGE_DEMOTE does not check interrupts (including NMIs) for basic
> > TDX (with or without Dynamic PAMT).
>
> The cover letter mentions that there is a new TDX module in planning, which
> disables the interrupt checking. I guess TDX module would need to have a
> interface to report the change, KVM then decides to enable huge page support or
> not for TDs?
Yes. But I guess detecting TDX module version or if it supports certain feature
is a generic problem. e.g., certain versions of TDX module have bugs in
zero-step mitigation and may block vCPU entering.
So, maybe it deserves a separate series?
> >
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > Co-developed-by: Yan Zhao <yan.y.zhao@...el.com>
> > Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> > ---
> > RFC v2:
> > - Refine the patch log (Rick).
> > - Do not handle TDX_INTERRUPTED_RESTARTABLE as the new TDX modules in
> > planning do not check interrupts for basic TDX.
> >
> > RFC v1:
> > - Rebased and split patch. Updated patch log.
> > ---
> > 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 f968b736871a..d2cf48e273d5 100644
> > --- a/arch/x86/include/asm/tdx.h
> > +++ b/arch/x86/include/asm/tdx.h
> > @@ -178,6 +178,8 @@ 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 580f14f64822..d941f083f741 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.c
> > +++ b/arch/x86/virt/vmx/tdx/tdx.c
> > @@ -1825,6 +1825,26 @@ 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,
>
> Nit: Is it better to use a var name that clearly tell that the page is used as a
> table page?
Yes, Thanks!
I also plan to do it (as well as for that tdx_spte_demote_private_spte() as
mentioned in
https://lore.kernel.org/all/aKKp3fyoYgaaqidm@yzhao56-desk.sh.intel.com).
> > + u64 *ext_err1, u64 *ext_err2)
> > +{
> > + struct tdx_module_args args = {
> > + .rcx = gpa | level,
> > + .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;
> > +
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(tdh_mem_page_demote);
> > +
> > u64 tdh_mr_extend(struct tdx_td *td, u64 gpa, u64 *ext_err1, u64 *ext_err2)
> > {
> > struct tdx_module_args args = {
> > diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> > index 096c78a1d438..a6c0fa53ece9 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.h
> > +++ b/arch/x86/virt/vmx/tdx/tdx.h
> > @@ -24,6 +24,7 @@
> > #define TDH_MNG_KEY_CONFIG 8
> > #define TDH_MNG_CREATE 9
> > #define TDH_MNG_RD 11
> > +#define TDH_MEM_PAGE_DEMOTE 15
> > #define TDH_MR_EXTEND 16
> > #define TDH_MR_FINALIZE 17
> > #define TDH_VP_FLUSH 18
>
>
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