linux-kernel - Re: [PATCH] KVM: x86/mmu: Only zap valid non-mirror roots in kvm_zap_gfn

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <Z2kp11RuI1zJe2t0@yzhao56-desk.sh.intel.com>
Date: Mon, 23 Dec 2024 17:13:59 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <seanjc@...gle.com>, <rick.p.edgecombe@...el.com>,
	<binbin.wu@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
	<kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86/mmu: Only zap valid non-mirror roots in
 kvm_zap_gfn_range()

On Sun, Dec 22, 2024 at 08:28:56PM +0100, Paolo Bonzini wrote:
> On Fri, Nov 15, 2024 at 9:50 AM Yan Zhao <yan.y.zhao@...el.com> wrote:
> > Sean also suggested making the self-snoop feature a hard dependency for
> > enabling TDX [2].
> >
> > That is because
> > - TDX shared EPT is able to reuse the memory type specified in VMX's code
> >   as long as guest MTRRs are not referenced.
> > - KVM does not call kvm_zap_gfn_range() when attaching/detaching
> >   non-coherent DMA devices when the CPU have feature self-snoop. [3]
> >
> > However, [3] cannot be guaranteed after commit 9d70f3fec144 ("Revert "KVM:
> > VMX: Always honor guest PAT on CPUs that support self-snoop"), which was
> > due to a regression with the bochsdrm driver.
> 
> I think we should treat honoring of guest PAT like zap-memslot-only,
> and make it a quirk that TDX disables. Making it a quirk adds a bit of
> complexity, but it documents why the code exists and it makes it easy
> for TDX to disable it.
Thanks! Will do in this way after the new year.