linux-kernel - Re: [PATCH V4 0/1] KVM: TDX: Decrease TDX VM shutdown time

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Message-ID: <aHEdg0jQp7xkOJp5@google.com>
Date: Fri, 11 Jul 2025 07:19:47 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: pbonzini@...hat.com, Adrian Hunter <adrian.hunter@...el.com>, kvm@...r.kernel.org, 
	rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com, 
	kai.huang@...el.com, reinette.chatre@...el.com, tony.lindgren@...ux.intel.com, 
	binbin.wu@...ux.intel.com, isaku.yamahata@...el.com, 
	linux-kernel@...r.kernel.org, yan.y.zhao@...el.com, chao.gao@...el.com
Subject: Re: [PATCH V4 0/1] KVM: TDX: Decrease TDX VM shutdown time

On Fri, Jul 11, 2025, Xiaoyao Li wrote:
> On 7/11/2025 9:05 PM, Sean Christopherson wrote:
> > On Fri, Jul 11, 2025, Xiaoyao Li wrote:
> > > On 6/26/2025 11:58 PM, Sean Christopherson wrote:
> > > > On Wed, Jun 25, 2025, Sean Christopherson wrote:
> > > > > On Wed, 11 Jun 2025 12:51:57 +0300, Adrian Hunter wrote:
> > > > > > Changes in V4:
> > > > > > 
> > > > > > 	Drop TDX_FLUSHVP_NOT_DONE change.  It will be done separately.
> > > > > > 	Use KVM_BUG_ON() instead of WARN_ON().
> > > > > > 	Correct kvm_trylock_all_vcpus() return value.
> > > > > > 
> > > > > > Changes in V3:
> > > > > > 	Refer:
> > > > > >               https://lore.kernel.org/r/aAL4dT1pWG5dDDeo@google.com
> > > > > > 
> > > > > > [...]
> > > > > 
> > > > > Applied to kvm-x86 vmx, thanks!
> > > > > 
> > > > > [1/1] KVM: TDX: Add sub-ioctl KVM_TDX_TERMINATE_VM
> > > > >         https://github.com/kvm-x86/linux/commit/111a7311a016
> > > > 
> > > > Fixed up to address a docs goof[*], new hash:
> > > > 
> > > >         https://github.com/kvm-x86/linux/commit/e4775f57ad51
> > > > 
> > > > [*] https://lore.kernel.org/all/20250626171004.7a1a024b@canb.auug.org.au
> > > 
> > > Hi Sean,
> > > 
> > > I think it's targeted for v6.17, right?
> > > 
> > > If so, do we need the enumeration for the new TDX ioctl? Yes, the userspace
> > > could always try and ignore the failure. But since the ship has not sailed,
> > > I would like to report it and hear your opinion.
> > 
> > Bugger, you're right.  It's sitting at the top of 'kvm-x86 vmx', so it should be
> > easy enough to tack on a capability.
> > 
> > This?
> 
> I'm wondering if we need a TDX centralized enumeration interface, e.g., new
> field in struct kvm_tdx_capabilities. I believe there will be more and more
> TDX new features, and assigning each a KVM_CAP seems wasteful.

Oh, yeah, that's a much better idea.  In addition to not polluting KVM_CAP, 

LOL, and we certainly have the capacity in the structure:

	__u64 reserved[250];

Sans documentation, something like so?

--
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 13da87c05098..70ffe6e8d216 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -963,6 +963,8 @@ struct kvm_tdx_cmd {
        __u64 hw_error;
 };
 
+#define KVM_TDX_CAP_TERMINATE_VM       _BITULL(0)
+
 struct kvm_tdx_capabilities {
        __u64 supported_attrs;
        __u64 supported_xfam;
@@ -972,7 +974,9 @@ struct kvm_tdx_capabilities {
        __u64 kernel_tdvmcallinfo_1_r12;
        __u64 user_tdvmcallinfo_1_r12;
 
-       __u64 reserved[250];
+       __u64 supported_caps;
+
+       __u64 reserved[249];
 
        /* Configurable CPUID bits for userspace */
        struct kvm_cpuid2 cpuid;
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index f4d4fd5cc6e8..783b1046f6c1 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -189,6 +189,8 @@ static int init_kvm_tdx_caps(const struct tdx_sys_info_td_conf *td_conf,
        if (!caps->supported_xfam)
                return -EIO;
 
+       caps->supported_caps = KVM_TDX_CAP_TERMINATE_VM;
+
        caps->cpuid.nent = td_conf->num_cpuid_config;
 
        caps->user_tdvmcallinfo_1_r11 =
--


Aha!  And if we squeeze in a patch for 6.16. to zero out the reserved array, we
can even avoid adding a capability to enumerate the TDX capability functionality.

--
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index f4d4fd5cc6e8..9c2997665762 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -181,6 +181,8 @@ static int init_kvm_tdx_caps(const struct tdx_sys_info_td_conf *td_conf,
 {
        int i;
 
+       memset(caps->reserved, 0, sizeof(caps->reserved));
+
        caps->supported_attrs = tdx_get_supported_attrs(td_conf);
        if (!caps->supported_attrs)
                return -EIO;
--