Re: [PATCH v2 10/19] target/riscv: remove kvm-stub.c

[Andrew Jones]

On Wed, Sep 06, 2023 at 12:23:19PM +0200, Philippe Mathieu-Daudé wrote:
> On 6/9/23 11:16, Daniel Henrique Barboza wrote:
> > This file is not needed for some time now. All the stubs implemented in
> > it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
> > kvm_enabled()' blocks that the compiler will rip it out in non-KVM
> > builds.
> > 
> > We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
> > All stubs are implemented as g_asserted_not_reached(), meaning that we
> > won't support them in non-KVM builds. This is done by other kvm headers
> > like kvm_arm.h and kvm_ppc.h.
> 
> Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?

Yes, I think your earlier suggestion that we always invoke kvm functions
from non-kvm files with a kvm_enabled() guard makes sense.

> 
> > Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> > ---
> >   target/riscv/kvm-stub.c  | 30 ------------------------------
> >   target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
> >   target/riscv/meson.build |  2 +-
> >   3 files changed, 32 insertions(+), 31 deletions(-)
> >   delete mode 100644 target/riscv/kvm-stub.c
> 
> 
> > diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
> > index f6501e68e2..c9ecd9a967 100644
> > --- a/target/riscv/kvm_riscv.h
> > +++ b/target/riscv/kvm_riscv.h
> > @@ -19,6 +19,7 @@
> >   #ifndef QEMU_KVM_RISCV_H
> >   #define QEMU_KVM_RISCV_H
> > +#ifdef CONFIG_KVM
> >   void kvm_riscv_cpu_add_kvm_properties(Object *obj);
> 
> At a glance kvm_riscv_cpu_add_kvm_properties() is.
> Keep the prototype declared (before #ifdef CONFIG_KVM) is enough for the
> compiler to elide it.

Yes, when building without CONFIG_KVM enabled it's actually better to not
have the stubs, since the compiler will catch an unguarded kvm function
call (assuming the kvm function is defined in a file which is only built
with CONFIG_KVM).

Unfortunately we don't have anything to protect developers from forgetting
the kvm_enabled() guard when building a QEMU which supports both TCG and
KVM. We could try to remember to put 'assert(kvm_enabled())' at the start
of each of these types of functions. It looks like mips does that for a
couple functions.

Thanks,
drew