linux-kernel - Re: [PATCH v19 070/130] KVM: TDX: TDP MMU TDX support

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Message-ID: <ZlbftscsqGQjWZqj@chenyu5-mobl2>
Date: Wed, 29 May 2024 15:56:38 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>
CC: Chao Gao <chao.gao@...el.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <isaku.yamahata@...il.com>, Paolo Bonzini
	<pbonzini@...hat.com>, <erdemaktas@...gle.com>, Sean Christopherson
	<seanjc@...gle.com>, Sagi Shahar <sagis@...gle.com>, Kai Huang
	<kai.huang@...el.com>, <chen.bo@...el.com>, <hang.yuan@...el.com>,
	<tina.zhang@...el.com>, Fengwei Yin <fengwei.yin@...el.com>,
	<isaku.yamahata@...ux.intel.com>
Subject: Re: [PATCH v19 070/130] KVM: TDX: TDP MMU TDX support

On 2024-05-28 at 17:58:59 -0700, Isaku Yamahata wrote:
> On Tue, May 28, 2024 at 05:55:19PM -0700,
> Isaku Yamahata <isaku.yamahata@...el.com> wrote:
> 
> > On Sun, May 26, 2024 at 04:45:15PM +0800,
> > Chen Yu <yu.c.chen@...el.com> wrote:
> > 
> > > On 2024-03-28 at 11:12:57 +0800, Chao Gao wrote:
> > > > >+#if IS_ENABLED(CONFIG_HYPERV)
> > > > >+static int vt_flush_remote_tlbs(struct kvm *kvm);
> > > > >+#endif
> > > > >+
> > > > > static __init int vt_hardware_setup(void)
> > > > > {
> > > > > 	int ret;
> > > > >@@ -49,11 +53,29 @@ static __init int vt_hardware_setup(void)
> > > > > 		pr_warn_ratelimited("TDX requires mmio caching.  Please enable mmio caching for TDX.\n");
> > > > > 	}
> > > > > 
> > > > >+#if IS_ENABLED(CONFIG_HYPERV)
> > > > >+	/*
> > > > >+	 * TDX KVM overrides flush_remote_tlbs method and assumes
> > > > >+	 * flush_remote_tlbs_range = NULL that falls back to
> > > > >+	 * flush_remote_tlbs.  Disable TDX if there are conflicts.
> > > > >+	 */
> > > > >+	if (vt_x86_ops.flush_remote_tlbs ||
> > > > >+	    vt_x86_ops.flush_remote_tlbs_range) {
> > > > >+		enable_tdx = false;
> > > > >+		pr_warn_ratelimited("TDX requires baremetal. Not Supported on VMM guest.\n");
> > > > >+	}
> > > > >+#endif
> > > > >+
> > > > > 	enable_tdx = enable_tdx && !tdx_hardware_setup(&vt_x86_ops);
> > > > > 	if (enable_tdx)
> > > > > 		vt_x86_ops.vm_size = max_t(unsigned int, vt_x86_ops.vm_size,
> > > > > 					   sizeof(struct kvm_tdx));
> > > > > 
> > > > >+#if IS_ENABLED(CONFIG_HYPERV)
> > > > >+	if (enable_tdx)
> > > > >+		vt_x86_ops.flush_remote_tlbs = vt_flush_remote_tlbs;
> > > > 
> > > > Is this hook necessary/beneficial to TDX?
> > > >
> > > 
> > > I think so.
> > > 
> > > We happended to encounter the following error and breaks the boot up:
> > > "SEAMCALL (0x000000000000000f) failed: 0xc0000b0800000001"
> > > 0xc0000b0800000001 indicates the TDX_TLB_TRACKING_NOT_DONE, and it is caused
> > > by page demotion but not yet doing a tlb shotdown by tlb track.
> > > 
> > > 
> > > It was found on my system the CONFIG_HYPERV is not set, and it makes
> > > kvm_arch_flush_remote_tlbs() not invoking tdx_track() before the
> > > tdh_mem_page_demote(), which caused the problem.
> > > 
> > > > if no, we can leave .flush_remote_tlbs as NULL. if yes, we should do:
> > > > 
> > > > struct kvm_x86_ops {
> > > > ...
> > > > #if IS_ENABLED(CONFIG_HYPERV) || IS_ENABLED(TDX...)
> > > > 	int  (*flush_remote_tlbs)(struct kvm *kvm);
> > > > 	int  (*flush_remote_tlbs_range)(struct kvm *kvm, gfn_t gfn,
> > > > 					gfn_t nr_pages);
> > > > #endif
> > > 
> > > If the flush_remote_tlbs implementation are both available in HYPERV and TDX,
> > > does it make sense to remove the config checks? I thought when commit 0277022a77a5
> > > was introduced, the only user of flush_remote_tlbs() is hyperv, and now
> > > there is TDX.
> > 
> > You don't like IS_ENABLED(CONFIG_HYPERV) || IS_ENABLED(CONFIG_TDX_HOST) in many
> > places?  Then, we can do something like the followings.  Although It would be
> > a bit ugly than the commit of 0277022a77a5, it's better to keep the intention
> > of it.
> > 
> 
> Ah, we have already __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE. We can use it.

Yes, and there is also __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS so we can use
ifdef __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE when needed.

thanks,
Chenyu
> -- 
> Isaku Yamahata <isaku.yamahata@...el.com>