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Date: Tue, 7 May 2024 09:27:45 +0530
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Subject: Re: [PATCH 2/3] x86/bus_lock: Add support for AMD
To: Jim Mattson <jmattson@google.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
 dave.hansen@linux.intel.com, seanjc@google.com, pbonzini@redhat.com,
 thomas.lendacky@amd.com, hpa@zytor.com, rmk+kernel@armlinux.org.uk,
 peterz@infradead.org, james.morse@arm.com, lukas.bulwahn@gmail.com,
 arjan@linux.intel.com, j.granados@samsung.com, sibs@chinatelecom.cn,
 nik.borisov@suse.com, michael.roth@amd.com, nikunj.dadhania@amd.com,
 babu.moger@amd.com, x86@kernel.org, kvm@vger.kernel.org,
 linux-kernel@vger.kernel.org, santosh.shukla@amd.com,
 ananth.narayan@amd.com, sandipan.das@amd.com,
 Ravi Bangoria <ravi.bangoria@amd.com>
References: <20240429060643.211-1-ravi.bangoria@amd.com>
 <20240429060643.211-3-ravi.bangoria@amd.com>
 <CALMp9eQzbNVJpuxp1orNswnyfKy=aFSPYFRnd3H7fbi0+NfDvw@mail.gmail.com>
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From: Ravi Bangoria <ravi.bangoria@amd.com>
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On 06-May-24 9:54 PM, Jim Mattson wrote:
> On Sun, Apr 28, 2024 at 11:08 PM Ravi Bangoria <ravi.bangoria@amd.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