linux-kernel - Re: [PATCH 4/4] arm64: mte: Use stage-2 NoTagAccess memory attribute if supported

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Message-ID: <yq5amsiocmb1.fsf@kernel.org>
Date: Mon, 28 Oct 2024 20:22:02 +0530
From: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, Suzuki K Poulose <Suzuki.Poulose@....com>,
	Steven Price <steven.price@....com>,
	Will Deacon <will@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Joey Gouly <joey.gouly@....com>,
	Zenghui Yu <yuzenghui@...wei.com>
Subject: Re: [PATCH 4/4] arm64: mte: Use stage-2 NoTagAccess memory
 attribute if supported


Hi Oliver,


Thanks for reviewing the changes.

Oliver Upton <oliver.upton@...ux.dev> writes:

> On Mon, Oct 28, 2024 at 03:10:14PM +0530, Aneesh Kumar K.V (Arm) wrote:
>

> NOTE: We could also use KVM_EXIT_MEMORY_FAULT for this. I chose to
> add a new EXIT type because this is arm64 specific exit type.
>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@...nel.org>
> ---

I have used KVM_EXIT_MEMORY_FAULT as part of the initial prototype.

>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 637efc055145..a8268a164c4d 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -178,6 +178,7 @@ struct kvm_xen_exit {
>>  #define KVM_EXIT_NOTIFY           37
>>  #define KVM_EXIT_LOONGARCH_IOCSR  38
>>  #define KVM_EXIT_MEMORY_FAULT     39
>> +#define KVM_EXIT_ARM_NOTAG_ACCESS 40
>>  
>>  /* For KVM_EXIT_INTERNAL_ERROR */
>>  /* Emulate instruction failed. */
>> @@ -446,6 +447,12 @@ struct kvm_run {
>>  			__u64 gpa;
>>  			__u64 size;
>>  		} memory_fault;
>> +		/* KVM_EXIT_ARM_NOTAG_ACCESS */
>> +		struct {
>> +			__u64 flags;
>> +			__u64 gpa;
>> +			__u64 size;
>> +		} notag_access;
>
> Can you please look into reusing the memory fault exit infrastructure?
>
> The entire point of that is for KVM to tell the VMM it cannot make
> forward progress because of ${SOMETHING} unexpected at the specified
> GPA. You can add a new flag that describes tag access.
>

The only reason I dropped the change was because the flag will be very much
arm64 specific. Based on your feedback, I will switch to
KVM_EXIT_MEMORY_FAULT in the next update.

-aneesh