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

[Borislav Petkov]

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?

>   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.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette