linux-kernel - Re: [RFC PATCH 1/2] KVM: arm64: nv: selftests: Add guest hypervisor test

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Message-ID: <86jza1ua7w.wl-maz@kernel.org>
Date: Fri, 07 Feb 2025 13:59:31 +0000
From: Marc Zyngier <maz@...nel.org>
To: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Cc: kvm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	oliver.upton@...ux.dev,
	joey.gouly@....com,
	suzuki.poulose@....com,
	darren@...amperecomputing.com,
	scott@...amperecomputing.com
Subject: Re: [RFC PATCH 1/2] KVM: arm64: nv: selftests: Add guest hypervisor test

On Fri, 07 Feb 2025 13:26:41 +0000,
Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com> wrote:
> 
> >> +	if (is_vcpu_nested(vcpu)) {
> >> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_CPTR_EL2), fpen);
> >> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_SCTLR_EL2), sctlr_el1);
> >> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TCR_EL2), tcr_el1);
> >> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MAIR_EL2), DEFAULT_MAIR_EL1);
> >> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TTBR0_EL2), ttbr0_el1);
> >> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TPIDR_EL2), vcpu->id);
> > 
> > How about some of the basics such as HCR_EL2, MDCR_EL2? A bunch of
> > things there do have an impact on how the guest behaves, and relying
> > on defaults feels like a bad idea.
> 
> Sure, I will try to have these registers also set to required value
> explicitly.
> 
> > 
> > This also assumes VHE, without trying to enforce it.
> 
> Ok, I will try to set specific bits of HCR_EL2 to force it run in VHE.
> 
> > 
> > Finally, how to you plan to make all the existing tests run as EL2
> > guests if TPIDR_EL1 isn't populated with the expected value? Surely
> > you need to change the read side...
> 
> OK, I have not yet tried running existing tests modifying to run as
> EL2 guests. I will try to run them modifying to run in vEL2.

You shouldn't try to modify them. Just make them take a parameter so
that the initialisation is done by configuring everything at EL2.

> 
> Should we modify them to run as EL2 guests by default, if the host
> supports/detected NV? or command line argument based run? either in
> El1(default) or in EL2?

EL1 by default.

> 
> BTW, I have also ran all existing tests on L1, most of the tests are
> passing(atleast I did not see any failure prints).
> 
> arm64/debug-exceptions is failing on L1 and needs to be
> debugged/fixed/skipped.
> arm64/arch_timer_edge_cases fails on both L0 and L1.

Then I guess you have some work to do to debug these problems, and it
once more means that NV is not ready for merging.

	M.

-- 
Without deviation from the norm, progress is not possible.