Re: [kvmtool PATCH v10 5/5] KVM: arm/arm64: Add a vcpu feature for pointer authentication

From: Amit Daniel Kachhap <amit.kachhap@arm.com>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-kernel@vger.kernel.org,
	Kristina Martsenko <kristina.martsenko@arm.com>,
	Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [kvmtool PATCH v10 5/5] KVM: arm/arm64: Add a vcpu feature for pointer authentication
Date: Tue, 28 May 2019 18:18:16 +0530	[thread overview]
Message-ID: <53ecc253-e9e0-a6ca-2540-fa85bd26bfc1@arm.com> (raw)
In-Reply-To: <20190528101128.GB28398@e103592.cambridge.arm.com>

Hi Dave,

On 5/28/19 3:41 PM, Dave Martin wrote:
> On Wed, Apr 24, 2019 at 02:41:21PM +0100, Dave Martin wrote:
>> On Wed, Apr 24, 2019 at 12:32:22PM +0530, Amit Daniel Kachhap wrote:
>>> Hi,
>>>
>>> On 4/23/19 9:16 PM, Dave Martin wrote:
> 
> [...]
> 
>>>>> diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
>>>>> index 7780251..acd1d5f 100644
>>>>> --- a/arm/kvm-cpu.c
>>>>> +++ b/arm/kvm-cpu.c
>>>>> @@ -68,6 +68,18 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>>>>>   		vcpu_init.features[0] |= (1UL << KVM_ARM_VCPU_PSCI_0_2);
>>>>>   	}
>>>>> +	/* Check Pointer Authentication command line arguments. */
>>>>> +	if (kvm->cfg.arch.enable_ptrauth && kvm->cfg.arch.disable_ptrauth)
>>>>> +		die("Both enable-ptrauth and disable-ptrauth option cannot be present");
>>>>
>>>> Preferably, print the leading dashes, the same as the user would see
>>>> on the command line (e.g., --enable-ptrauth, --disable-ptrauth).
>>>>
>>>> For brevity, we could write something like:
>>>>
>>>> 		die("--enable-ptrauth conflicts with --disable-ptrauth");
> 
> [...]
> 
>>>>> @@ -106,8 +118,12 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>>>>>   			die("Unable to find matching target");
>>>>>   	}
>>>>> -	if (err || target->init(vcpu))
>>>>> -		die("Unable to initialise vcpu");
>>>>> +	if (err || target->init(vcpu)) {
>>>>> +		if (kvm->cfg.arch.enable_ptrauth)
>>>>> +			die("Unable to initialise vcpu with pointer authentication feature");
>>>>
>>>> We don't special-case this error message for any other feature yet:
>>>> there are a variety of reasons why we might have failed, so suggesting
>>>> that the failure is something to do with ptrauth may be misleading to
>>>> the user.
>>>>
>>>> If we want to be more informative, we could do something like the
>>>> following:
>>>>
>>>> 	bool supported;
>>>>
>>>> 	supported = kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
>>>> 		    kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC);
>>>>
>>>> 	if (kvm->cfg.arch.enable_ptrauth && !supported)
>>>> 		die("--enable-ptrauth not supported on this host");
>>>>
>>>> 	if (supported && !kvm->cfg.arch.disable_ptrauth)
>>>> 		vcpu_init.features[0] |= ARM_VCPU_PTRAUTH_FEATURE;
>>>>
>>>> 	/* ... */
>>>>
>>>> 	if (err || target->init(vcpu))
>>>> 		die("Unable to initialise vcpu");
>>>>
>>>> We don't do this for any other feature today, but since it helps the
>>>> user to understand what went wrong it's probably a good idea.
>>> Yes this is more clear. As Mark has picked the core guest ptrauth patches. I
>>> will post this changes as standalone.
>>
>> Sounds good.  (I also need to do that separately for SVE...)
> 
> Were you planning to repost this?
> 
> Alternatively, I can fix up the diagnostic messages discussed here and
> post it together with the SVE support.  I'll do that locally for now,
> but let me know what you plan to do.  I'd like to get the SVE support
> posted soon so that people can test it.
I will clean up the print messages as you suggested and repost it shortly.

Thanks,
Amit Daniel
> 
> Cheers
> ---Dave
> 
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