linux-kernel - Re: [PATCH 2/3] x86/bus_lock: Add support for AMD

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Date: Tue, 7 May 2024 09:27:45 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: Jim Mattson <jmattson@...gle.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, seanjc@...gle.com, pbonzini@...hat.com,
 thomas.lendacky@....com, hpa@...or.com, rmk+kernel@...linux.org.uk,
 peterz@...radead.org, james.morse@....com, lukas.bulwahn@...il.com,
 arjan@...ux.intel.com, j.granados@...sung.com, sibs@...natelecom.cn,
 nik.borisov@...e.com, michael.roth@....com, nikunj.dadhania@....com,
 babu.moger@....com, x86@...nel.org, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, santosh.shukla@....com,
 ananth.narayan@....com, sandipan.das@....com,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH 2/3] x86/bus_lock: Add support for AMD

On 06-May-24 9:54 PM, Jim Mattson wrote:
> On Sun, Apr 28, 2024 at 11:08 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
>>
>> Upcoming AMD uarch will support Bus Lock Detect (called Bus Lock Trap
>> in AMD docs). Add support for the same in Linux. Bus Lock Detect is
>> enumerated with cpuid CPUID Fn0000_0007_ECX_x0 bit [24 / BUSLOCKTRAP].
>> It can be enabled through MSR_IA32_DEBUGCTLMSR. When enabled, hardware
>> clears DR6[11] and raises a #DB exception on occurrence of Bus Lock if
>> CPL > 0. More detail about the feature can be found in AMD APM[1].
>>
>> [1]: AMD64 Architecture Programmer's Manual Pub. 40332, Rev. 4.07 - June
>>      2023, Vol 2, 13.1.3.6 Bus Lock Trap
>>      https://bugzilla.kernel.org/attachment.cgi?id=304653
> 
> Is there any chance of getting something similar to Intel's "VMM
> bus-lock detection," which causes a trap-style VM-exit on a bus lock
> event?

You are probably asking about "Bus Lock Threshold". Please see
"15.14.5 Bus Lock Threshold" in the same doc. fwiw, Bus Lock Threshold
is of fault style.

Thanks,
Ravi