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From: Andy Lutomirski <luto@kernel.org>
To: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Tony Luck <tony.luck@intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>
Subject: Re: [PATCH v9 3/8] x86/split_lock: Introduce flag X86_FEATURE_SLD_FATAL and drop sld_state
Date: Sat, 9 May 2020 22:14:02 -0700	[thread overview]
Message-ID: <CALCETrXwtj5rhVM6YYNEDeDqT3eKFNkGFCgSB_hUd7aOYBFXmw@mail.gmail.com> (raw)
In-Reply-To: <20200509110542.8159-4-xiaoyao.li@intel.com>

On Fri, May 8, 2020 at 8:03 PM Xiaoyao Li <xiaoyao.li@intel.com> wrote:
>
> Introduce a synthetic feature flag X86_FEATURE_SLD_FATAL, which means
> kernel is in sld_fatal mode if set.
>
> Now sld_state is not needed any more that the state of SLD can be
> inferred from X86_FEATURE_SPLIT_LOCK_DETECT and X86_FEATURE_SLD_FATAL.

Is it too much to ask for Intel to actually allocate and define a
CPUID bit that means "this CPU *always* sends #AC on a split lock"?
This would be a pure documentation change, but it would make this
architectural rather than something that each hypervisor needs to hack
up.

Meanwhile, I don't see why adding a cpufeature flag is worthwhile to
avoid a less bizarre global variable.  There's no performance issue
here, and the old code looked a lot more comprehensible than the new
code.

  reply	other threads:[~2020-05-10  5:14 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-09 11:05 [PATCH v9 0/8] KVM: Add virtualization support of split lock detection Xiaoyao Li
2020-05-09 11:05 ` [PATCH v9 1/8] x86/split_lock: Rename TIF_SLD to TIF_SLD_DISABLED Xiaoyao Li
2020-05-09 11:05 ` [PATCH v9 2/8] x86/split_lock: Remove bogus case in handle_guest_split_lock() Xiaoyao Li
2020-05-09 11:05 ` [PATCH v9 3/8] x86/split_lock: Introduce flag X86_FEATURE_SLD_FATAL and drop sld_state Xiaoyao Li
2020-05-10  5:14   ` Andy Lutomirski [this message]
2020-05-11 18:17     ` Sean Christopherson
2020-05-09 11:05 ` [PATCH v9 4/8] x86/split_lock: Introduce split_lock_virt_switch() and two wrappers Xiaoyao Li
2020-05-09 11:05 ` [PATCH v9 5/8] x86/kvm: Introduce paravirt split lock detection enumeration Xiaoyao Li
2020-05-09 11:05 ` [PATCH v9 6/8] KVM: VMX: Enable MSR TEST_CTRL for guest Xiaoyao Li
2020-05-09 11:05 ` [PATCH v9 7/8] KVM: VMX: virtualize split lock detection Xiaoyao Li
2020-05-09 11:05 ` [PATCH v9 8/8] x86/split_lock: Enable split lock detection initialization when running as an guest on KVM Xiaoyao Li
2020-05-10  5:15   ` Andy Lutomirski
2020-05-11  1:11     ` Xiaoyao Li
2020-05-18  1:27 ` [PATCH v9 0/8] KVM: Add virtualization support of split lock detection Xiaoyao Li
2020-05-26  6:19   ` Xiaoyao Li
2020-07-01  2:46 ` Xiaoyao Li

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