linux-kernel - Re: [PATCH RFC v2 3/3] riscv: KVM: Add Svukte extension support for Guest/VM

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Message-ID: <CAHibDywpKUE7r4UfcudDSBZCM=JAC5s40uf+PwQE+oMvZy4aVA@mail.gmail.com>
Date: Mon, 4 Nov 2024 15:44:21 +0800
From: Max Hsu <max.hsu@...ive.com>
To: Anup Patel <anup@...infault.org>
Cc: Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Atish Patra <atishp@...shpatra.org>, Palmer Dabbelt <palmer@...ive.com>, 
	linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	kvm-riscv@...ts.infradead.org, Samuel Holland <samuel.holland@...ive.com>
Subject: Re: [PATCH RFC v2 3/3] riscv: KVM: Add Svukte extension support for Guest/VM

Hi Anup,

Thank you for the suggestion.

I’m not entirely sure if I fully understand it, but I believe the
hypervisor should be able to disable the Svukte extension.

Inside the switch-case of kvm_riscv_vcpu_isa_disable_allowed(),
the default case breaks and returns true.

So that means when the KVM_RISCV_ISA_EXT_SVUKTE passed into
kvm_riscv_vcpu_isa_disable_allowed() it will return true.

If I've misunderstood, please let me know.

Best regards,
Max Hsu

On Fri, Oct 25, 2024 at 3:17 AM Anup Patel <anup@...infault.org> wrote:
>
> On Fri, Sep 27, 2024 at 7:12 PM Max Hsu <max.hsu@...ive.com> wrote:
> >
> > Add KVM ISA extension ONE_REG interface to allow VMM tools to
> > detect and enable Svukte extension for Guest/VM.
> >
> > Reviewed-by: Samuel Holland <samuel.holland@...ive.com>
> > Signed-off-by: Max Hsu <max.hsu@...ive.com>
> > ---
> >  arch/riscv/include/uapi/asm/kvm.h | 1 +
> >  arch/riscv/kvm/vcpu_onereg.c      | 1 +
> >  2 files changed, 2 insertions(+)
> >
> > diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> > index e97db3296456e19f79ca02e4c4f70ae1b4abb48b..41b466b7ffaec421e8389d3f5b178580091a2c98 100644
> > --- a/arch/riscv/include/uapi/asm/kvm.h
> > +++ b/arch/riscv/include/uapi/asm/kvm.h
> > @@ -175,6 +175,7 @@ enum KVM_RISCV_ISA_EXT_ID {
> >         KVM_RISCV_ISA_EXT_ZCF,
> >         KVM_RISCV_ISA_EXT_ZCMOP,
> >         KVM_RISCV_ISA_EXT_ZAWRS,
> > +       KVM_RISCV_ISA_EXT_SVUKTE,
> >         KVM_RISCV_ISA_EXT_MAX,
> >  };
> >
> > diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
> > index b319c4c13c54ce22d2a7552f4c9f256a0c50780e..67237d6e53882a9fcd2cf265aa1704f25cc4a701 100644
> > --- a/arch/riscv/kvm/vcpu_onereg.c
> > +++ b/arch/riscv/kvm/vcpu_onereg.c
> > @@ -41,6 +41,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
> >         KVM_ISA_EXT_ARR(SVINVAL),
> >         KVM_ISA_EXT_ARR(SVNAPOT),
> >         KVM_ISA_EXT_ARR(SVPBMT),
> > +       KVM_ISA_EXT_ARR(SVUKTE),
> >         KVM_ISA_EXT_ARR(ZACAS),
> >         KVM_ISA_EXT_ARR(ZAWRS),
> >         KVM_ISA_EXT_ARR(ZBA),
>
> The KVM_RISCV_ISA_EXT_SVUKTE should be added to the
> switch-case in kvm_riscv_vcpu_isa_disable_allowed() because
> hypervisor seems to have no way to disable Svukte for the Guest
> when it's available on the Host.
>
> Regards,
> Anup