linux-kernel - Re: [PATCH v3 17/17] KVM: x86/tdp_mmu: Take root types for kvm_tdp_mmu_invalidate_all

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Message-ID: <a727eb488b69c9674e8ecc2d099aec00af58fa7c.camel@intel.com>
Date: Thu, 18 Jul 2024 15:55:33 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "Gao, Chao" <chao.gao@...el.com>, "isaku.yamahata@...ux.intel.com"
	<isaku.yamahata@...ux.intel.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "dmatlack@...gle.com" <dmatlack@...gle.com>, "Zhao,
 Yan Y" <yan.y.zhao@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 17/17] KVM: x86/tdp_mmu: Take root types for
 kvm_tdp_mmu_invalidate_all_roots()

On Thu, 2024-07-18 at 08:28 -0700, Isaku Yamahata wrote:
> Although it's a bit late, it's for record.
> 
> It's to optimize the destruction Secure-EPT.  Free HKID early and destruct
> Secure-EPT by TDH.PHYMEM.PAGE.RECLAIM().  QEMU doesn't close any KVM file
> descriptors on exit. (gmem fd references KVM VM fd. so vm destruction happens
> after all gmem fds are closed.  Closing gmem fd causes secure-EPT zapping
> befure
> releasing HKID.)
> 
> Because we're ignoring such optimization for now, we can simply defer
> releasing
> HKID following Seans's call.

Thanks for the background.

> 
> 
> > But static_call_cond(kvm_x86_vm_destroy) happens before kvm_destroy_vcpus,
> > so we
> > could maybe actually just do the tdx_mmu_release_hkid() part there. Then
> > drop
> > the flush_shadow_all_private x86 op. See the (not thoroughly checked) diff
> > at
> > the bottom of this mail.
> 
> Yep, we can release HKID at vm destruction with potential too slow zapping of
> Secure-EPT.  The following change basically looks good to me.
> (The callback for Secure-EPT can be simplified.)