linux-kernel - Re: [PATCH v3 03/14] KVM: selftests: Return a value from vcpu_get

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Message-ID: <ZyTpwwm0s89iU9Pk@google.com>
Date: Fri, 1 Nov 2024 07:48:00 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Mark Brown <broonie@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Anup Patel <anup@...infault.org>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Paolo Bonzini <pbonzini@...hat.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Andrew Jones <ajones@...tanamicro.com>, James Houghton <jthoughton@...gle.com>, 
	David Woodhouse <dwmw@...zon.co.uk>, linux-next@...r.kernel.org
Subject: Re: [PATCH v3 03/14] KVM: selftests: Return a value from
 vcpu_get_reg() instead of using an out-param

On Fri, Nov 01, 2024, Mark Brown wrote:
> On Wed, Oct 09, 2024 at 08:49:42AM -0700, Sean Christopherson wrote:
> > Return a uint64_t from vcpu_get_reg() instead of having the caller provide
> > a pointer to storage, as none of the vcpu_get_reg() usage in KVM selftests
> > accesses a register larger than 64 bits, and vcpu_set_reg() only accepts a
> > 64-bit value.  If a use case comes along that needs to get a register that
> > is larger than 64 bits, then a utility can be added to assert success and
> > take a void pointer, but until then, forcing an out param yields ugly code
> > and prevents feeding the output of vcpu_get_reg() into vcpu_set_reg().
> 
> This commit, which is in today's -next as 5c6c7b71a45c9c, breaks the
> build on arm64:
> 
> aarch64/psci_test.c: In function ‘host_test_system_off2’:
> aarch64/psci_test.c:247:9: error: too many arguments to function ‘vcpu_get_reg’
>   247 |         vcpu_get_reg(target, KVM_REG_ARM_PSCI_VERSION, &psci_version);
>       |         ^~~~~~~~~~~~
> In file included from aarch64/psci_test.c:18:
> include/kvm_util.h:705:24: note: declared here
>   705 | static inline uint64_t vcpu_get_reg(struct kvm_vcpu *vcpu, uint64_t id)
>       |                        ^~~~~~~~~~~~
> At top level:
> cc1: note: unrecognized command-line option ‘-Wno-gnu-variable-sized-type-not-at
> -end’ may have been intended to silence earlier diagnostics
> 
> since the updates done to that file did not take account of 72be5aa6be4
> ("KVM: selftests: Add test for PSCI SYSTEM_OFF2") which has been merged
> in the kvm-arm64 tree.

Bugger.  In hindsight, it's obvious that of course arch selftests would add usage
of vcpu_get_reg().

Unless someone has a better idea, I'll drop the series from kvm-x86, post a new
version that applies on linux-next, and then re-apply the series just before the
v6.13 merge window (rinse and repeat as needed if more vcpu_get_reg() users come
along).

That would be a good oppurtunity to do the $(ARCH) directory switch[*] too, e.g.
have a "selftests_late" or whatever topic branch.

Sorry for the pain Mark, you've been playing janitor for us too much lately.

[*] https://lore.kernel.org/all/20240826190116.145945-1-seanjc@google.com