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From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Xiaoyao Li <xiaoyao.li@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Fenghua Yu <fenghua.yu@intel.com>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>, H Peter Anvin <hpa@zytor.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Radim Krcmar <rkrcmar@redhat.com>,
	Ashok Raj <ashok.raj@intel.com>, Tony Luck <tony.luck@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
	Ravi V Shankar <ravi.v.shankar@intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
	kvm@vger.kernel.org
Subject: Re: [PATCH v9 09/17] x86/split_lock: Handle #AC exception for split lock
Date: Wed, 16 Oct 2019 17:43:53 +0200	[thread overview]
Message-ID: <d235ed9a-314c-705c-691f-b31f2f8fa4e8@redhat.com> (raw)
In-Reply-To: <20191016154116.GA5866@linux.intel.com>

On 16/10/19 17:41, Sean Christopherson wrote:
> On Wed, Oct 16, 2019 at 04:08:14PM +0200, Paolo Bonzini wrote:
>> SIGBUS (actually a new KVM_EXIT_INTERNAL_ERROR result from KVM_RUN is
>> better, but that's the idea) is for when you're debugging guests.
>> Global disable (or alternatively, disable SMT) is for production use.
> 
> Alternatively, for guests without split-lock #AC enabled, what if KVM were
> to emulate the faulting instruction with split-lock detection temporarily
> disabled?

Yes we can get fancy, but remember that KVM is not yet supporting
emulation of locked instructions.  Adding it is possible but shouldn't
be in the critical path for the whole feature.

How would you disable split-lock detection temporarily?  Just tweak
MSR_TEST_CTRL for the time of running the one instruction, and cross
fingers that the sibling doesn't notice?

Thanks,

Paolo

> The emulator can presumably handle all such lock instructions, and an
> unhandled instruction would naturally exit to userspace.
> 
> The latency of VM-Enter+VM-Exit should be enough to guard against DoS from
> a malicious guest.  KVM could also artificially rate-limit a guest that is
> generating copious amounts of split-lock #ACs.
> 


  reply	other threads:[~2019-10-16 15:43 UTC|newest]

Thread overview: 85+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-18 22:41 [PATCH v9 00/17] x86/split_lock: Enable split lock detection Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 01/17] x86/common: Align cpu_caps_cleared and cpu_caps_set to unsigned long Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 02/17] drivers/net/b44: Align pwol_mask to unsigned long for better performance Fenghua Yu
2019-06-24 15:12   ` David Laight
2019-06-24 18:43     ` Paolo Bonzini
2019-06-18 22:41 ` [PATCH v9 03/17] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access Fenghua Yu
2019-06-24 15:12   ` David Laight
2019-06-25 23:54     ` Fenghua Yu
2019-06-26 19:15       ` Thomas Gleixner
2019-06-18 22:41 ` [PATCH v9 04/17] x86/msr-index: Define MSR_IA32_CORE_CAP and split lock detection bit Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 05/17] x86/cpufeatures: Enumerate MSR_IA32_CORE_CAP Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 06/17] x86/split_lock: Enumerate split lock detection by MSR_IA32_CORE_CAP Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 07/17] x86/split_lock: Enumerate split lock detection on Icelake mobile processor Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 08/17] x86/split_lock: Define MSR TEST_CTL register Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 09/17] x86/split_lock: Handle #AC exception for split lock Fenghua Yu
2019-06-26 20:20   ` Thomas Gleixner
2019-06-26 20:36     ` Fenghua Yu
2019-06-26 21:47       ` Thomas Gleixner
2019-09-25 18:09         ` Sean Christopherson
2019-10-16  6:58           ` Xiaoyao Li
2019-10-16  9:29           ` Thomas Gleixner
2019-10-16 15:59             ` Sean Christopherson
2019-10-16  9:40           ` Paolo Bonzini
2019-10-16  9:47             ` Thomas Gleixner
2019-10-16 10:16               ` Paolo Bonzini
2019-10-16 11:23                 ` Xiaoyao Li
2019-10-16 11:26                   ` Paolo Bonzini
2019-10-16 13:13                     ` Xiaoyao Li
2019-10-16 14:43                       ` Thomas Gleixner
2019-10-16 15:37                         ` Paolo Bonzini
2019-10-16 16:25                           ` Xiaoyao Li
2019-10-16 16:38                             ` Paolo Bonzini
2019-10-17 12:29                           ` [RFD] x86/split_lock: Request to Intel Thomas Gleixner
2019-10-17 17:23                             ` Sean Christopherson
2019-10-17 21:31                               ` Thomas Gleixner
2019-10-17 23:38                                 ` Sean Christopherson
2019-10-17 23:28                             ` Luck, Tony
2019-10-18 10:45                               ` David Laight
2019-10-18 21:03                                 ` hpa
2019-10-18  2:36                             ` Xiaoyao Li
2019-10-18  9:02                               ` Thomas Gleixner
2019-10-18 10:20                                 ` Xiaoyao Li
2019-10-18 10:43                                   ` Peter Zijlstra
2019-10-16 11:49                 ` [PATCH v9 09/17] x86/split_lock: Handle #AC exception for split lock Thomas Gleixner
2019-10-16 11:58                   ` Paolo Bonzini
2019-10-16 13:51                     ` Xiaoyao Li
2019-10-16 14:08                       ` Paolo Bonzini
2019-10-16 14:14                         ` David Laight
2019-10-16 15:03                           ` Thomas Gleixner
2019-10-16 15:41                         ` Sean Christopherson
2019-10-16 15:43                           ` Paolo Bonzini [this message]
2019-10-16 16:23                             ` Sean Christopherson
2019-10-16 17:42                               ` Sean Christopherson
2019-10-17  1:23                                 ` Xiaoyao Li
2019-10-21 13:06                                   ` Paolo Bonzini
2019-10-21 13:03                                 ` Paolo Bonzini
2019-10-21 13:02                               ` Paolo Bonzini
2019-10-16 14:50                       ` Thomas Gleixner
2019-06-18 22:41 ` [PATCH v9 10/17] kvm/x86: Emulate MSR IA32_CORE_CAPABILITY Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 11/17] kvm/vmx: Emulate MSR TEST_CTL Fenghua Yu
2019-06-27  2:24   ` Xiaoyao Li
2019-06-27  7:12     ` Thomas Gleixner
2019-06-27  7:58       ` Xiaoyao Li
2019-06-27 12:11         ` Thomas Gleixner
2019-06-27 12:22           ` Xiaoyao Li
2019-06-18 22:41 ` [PATCH v9 12/17] x86/split_lock: Enable split lock detection by default Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 13/17] x86/split_lock: Disable split lock detection by kernel parameter "nosplit_lock_detect" Fenghua Yu
2019-06-26 20:34   ` Thomas Gleixner
2019-06-26 20:37     ` Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 14/17] x86/split_lock: Add a debugfs interface to enable/disable split lock detection during run time Fenghua Yu
2019-06-26 21:37   ` Thomas Gleixner
2019-06-18 22:41 ` [PATCH v9 15/17] x86/split_lock: Add documentation for split lock detection interface Fenghua Yu
2019-06-26 21:51   ` Thomas Gleixner
2019-06-18 22:41 ` [PATCH v9 16/17] x86/split_lock: Reorganize few header files in order to call WARN_ON_ONCE() in atomic bit ops Fenghua Yu
2019-06-18 22:41 ` [PATCH v9 17/17] x86/split_lock: Warn on unaligned address in atomic bit operations Fenghua Yu
2019-06-26 22:00   ` Thomas Gleixner
2019-09-16 22:39 ` [PATCH 0/3] Fix some 4-byte vs. 8-byte alignment issues Tony Luck
2019-09-16 22:39   ` [PATCH 1/3] x86/common: Align cpu_caps_cleared and cpu_caps_set to unsigned long Tony Luck
2019-11-15 19:26     ` [tip: x86/cpu] x86/cpu: " tip-bot2 for Fenghua Yu
2019-09-16 22:39   ` [PATCH 2/3] drivers/net/b44: Align pwol_mask to unsigned long for better performance Tony Luck
2019-09-16 22:39   ` [PATCH 3/3] x86/split_lock: Align the x86_capability array to size of unsigned long Tony Luck
2019-09-17  8:29     ` David Laight
2019-09-17 19:14       ` Luck, Tony
2019-09-18  8:54         ` David Laight
2019-11-15 19:26     ` [tip: x86/cpu] x86/cpu: " tip-bot2 for Fenghua Yu

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