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

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Message-ID: <20190528101128.GB28398@e103592.cambridge.arm.com>
Date:   Tue, 28 May 2019 11:11:31 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Amit Daniel Kachhap <amit.kachhap@....com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Kristina Martsenko <kristina.martsenko@....com>,
        Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
Subject: Re: [kvmtool PATCH v10 5/5] KVM: arm/arm64: Add a vcpu feature for
 pointer authentication

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.

Cheers
---Dave