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From: Andy Lutomirski <luto@amacapital.net>
To: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: VMX: Extend VMX's #AC handding
Date: Thu, 30 Jan 2020 07:18:14 -0800	[thread overview]
Message-ID: <4A8E14B3-1914-4D0C-A43A-234717179408@amacapital.net> (raw)
In-Reply-To: <20200130121939.22383-3-xiaoyao.li@intel.com>



> On Jan 30, 2020, at 4:24 AM, Xiaoyao Li <xiaoyao.li@intel.com> wrote:
> 
> There are two types of #AC can be generated in Intel CPUs:
> 1. legacy alignment check #AC;
> 2. split lock #AC;
> 
> Legacy alignment check #AC can be injected to guest if guest has enabled
> alignemnet check.
> 
> When host enables split lock detection, i.e., split_lock_detect!=off,
> guest will receive an unexpected #AC when there is a split_lock happens in
> guest since KVM doesn't virtualize this feature to guest.
> 
> Since the old guests lack split_lock #AC handler and may have split lock
> buges. To make guest survive from split lock, applying the similar policy
> as host's split lock detect configuration:
> - host split lock detect is sld_warn:
>   warning the split lock happened in guest, and disabling split lock
>   detect around VM-enter;
> - host split lock detect is sld_fatal:
>   forwarding #AC to userspace. (Usually userspace dump the #AC
>   exception and kill the guest).

A correct userspace implementation should, with a modern guest kernel, forward the exception. Otherwise you’re introducing a DoS into the guest if the guest kernel is fine but guest userspace is buggy.

What’s the intended behavior here?

  reply	other threads:[~2020-01-30 15:18 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-30 12:19 [PATCH 0/2] kvm: split_lock: Fix emulator and extend #AC handler Xiaoyao Li
2020-01-30 12:19 ` [PATCH 1/2] KVM: x86: Emulate split-lock access as a write Xiaoyao Li
2020-01-30 12:31   ` David Laight
2020-01-30 15:16     ` Andy Lutomirski
2020-01-31 20:01       ` Sean Christopherson
2020-02-04 14:47         ` Vitaly Kuznetsov
2020-02-10 21:59           ` Sean Christopherson
2020-01-30 12:19 ` [PATCH 2/2] KVM: VMX: Extend VMX's #AC handding Xiaoyao Li
2020-01-30 15:18   ` Andy Lutomirski [this message]
2020-01-30 16:29     ` Xiaoyao Li
2020-01-30 17:16       ` Andy Lutomirski
2020-01-31  7:22         ` Xiaoyao Li
2020-01-31 15:37           ` Andy Lutomirski
2020-01-31 17:47             ` Xiaoyao Li
2020-01-31 20:17               ` Sean Christopherson
2020-01-31 20:57                 ` Andy Lutomirski
2020-01-31 21:04                   ` Sean Christopherson
2020-01-31 21:33                     ` Andy Lutomirski
2020-02-01 16:58                       ` Xiaoyao Li
2020-02-01 17:56                         ` Andy Lutomirski
2020-02-02  4:33                           ` Xiaoyao Li
2020-02-03 18:49                             ` Andy Lutomirski
2020-02-04  6:03                               ` Sean Christopherson

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