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Message-ID: <YWhG+UcaRyNptzw9@google.com>
Date: Thu, 14 Oct 2021 15:04:25 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Sathyanarayanan Kuppuswamy
<sathyanarayanan.kuppuwamy@...ux.intel.com>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
David Hildenbrand <david@...hat.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Dave Hansen <dave.hansen@...el.com>,
Tony Luck <tony.luck@...el.com>,
Dan Williams <dan.j.williams@...el.com>,
Andi Kleen <ak@...ux.intel.com>,
Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 6/6] x86/split_lock: Fix the split lock #AC handling
when running as guest
On Thu, Oct 14, 2021, Xiaoyao Li wrote:
> On 10/14/2021 5:32 AM, Sathyanarayanan Kuppuswamy wrote:
> > + Xiaoyao
> >
> > On 10/13/21 1:30 PM, Sean Christopherson wrote:
> > > On Tue, Oct 05, 2021, Kuppuswamy Sathyanarayanan wrote:
> > > > From: Xiaoyao Li <xiaoyao.li@...el.com>
> > > >
> > > > If running as guest and hypervisor enables
> > > > MSR_TEST_CTRL.SPLIT_LOCK_DETECT during its running, it can get split
> > > > lock #AC even though sld_state is sld_off.
> > > That's a hypervisor bug, no? The hypervisor should never inject a fault
> > > that the guest cannot reasonably expect.
>
> What if hypervisor doesn't intercept #AC and host enables SPLIT_LOCK_DETECT
> during guest running? That's exactly the case TDX is facing.
That's a hypervisor bug. Since it sounds like the TDX Module buries its head in
the sand for split-lock #AC, KVM should refuse to run TDX guests if split-lock #AC
is enabled. Ideally the TDX Module would provide support for conditionally
intercepting #AC, e.g. intercept and re-inject "normal" #AC, and exit to the VMM
for split-lock #AC. That would give VMMs the option of enabling split-lock
detection in fatal mode for guests.
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