Re: [PATCH 1/4] x86/msr: Define new bits in TSX_FORCE_ABORT MSR

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Jonathan Corbet <corbet@lwn.net>,
	Peter Zijlstra <peterz@infradead.org>,
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	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Randy Dunlap <rdunlap@infradead.org>,
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	"Maciej W. Rozycki" <macro@orcam.me.uk>,
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Subject: Re: [PATCH 1/4] x86/msr: Define new bits in TSX_FORCE_ABORT MSR
Date: Fri, 11 Jun 2021 14:31:29 -0700	[thread overview]
Message-ID: <20210611213129.py2jyfzy37czegkm@gupta-dev2.localdomain> (raw)
In-Reply-To: <YMMhTwR7lJvA/9nu@zn.tnic>

On 11.06.2021 10:39, Borislav Petkov wrote:
>On Wed, Jun 09, 2021 at 01:58:02PM -0700, Pawan Gupta wrote:
>> Intel client processors that support IA32_TSX_FORCE_ABORT MSR related to
>> perf counter interaction [1] received a microcode update that deprecates
>> Transactional Synchronization Extension (TSX) feature. MSR
>> IA32_TSX_FORCE_ABORT bit FORCE_ABORT_RTM now defaults to 1, writes to
>> this bit are ignored. A new bit TSX_CPUID_CLEAR clears the TSX related
>> CPUID bits.
>>
>> Below is the summary of changes to IA32_TSX_FORCE_ABORT MSR:
>>
>>   Bit 0: FORCE_ABORT_RTM (legacy bit, new default=1) Status bit that
>>   indicates if RTM transactions are always aborted. This bit is
>>   essentially !SDV_ENABLE_RTM(Bit 2). Writes to this bit are ignored.
>>
>>   Bit 1: TSX_CPUID_CLEAR (new bit, default=0) When set, CPUID.HLE = 0
>>   and CPUID.RTM = 0.
>>
>>   Bit 2: SDV_ENABLE_RTM (new bit, default=0) When clear, XBEGIN will
>>   always abort with EAX code 0. When set, XBEGIN will not be forced to
>>   abort (but will always abort in SGX enclaves). This bit is intended to
>>   be SDV-only. If this bit is set transactional atomicity correctness is
>
>SDV?

Sorry should have expanded this. It stands for Software Development
Vehicle (SDV), i.e. developer systems.

>>   not certain.
>>
>> Performance monitoring counter 3 is usable in all cases, regardless of
>> the value of above bits.
>>
>> A new CPUID bit CPUID.RTM_ALWAYS_ABORT (CPUID 7.EDX[11]) is added to
>> indicate the status of always abort behavior.
>>
>> Define these new CPUID and MSR bits.
>>
>> [1] Performance Monitoring Impact of Intel® Transactional Synchronization Extension Memory
>>     http://cdrdv2.intel.com/v1/dl/getContent/604224
>
>That link does not look stable enough to put in commit messages.
>Besides, you've said it all in the commit message already.

The important part is the Document ID 604224. I can remove the link
completely, or add the document ID to it, whatever you suggest:

	[1] Performance Monitoring Impact of Intel® Transactional Synchronization Extension Memory
	    http://cdrdv2.intel.com/v1/dl/getContent/604224 (Document ID 604224).
							     ^^^^^^^^^^^^^^^^^^

Thanks,
Pawan