linux-kernel - Re: [PATCH v2 5/7] RISC-V: KVM: Reduce KVM_MAX

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Date:   Mon, 9 May 2022 11:03:34 +0530
From:   Anup Patel <anup@...infault.org>
To:     Atish Patra <atishp@...shpatra.org>
Cc:     Anup Patel <apatel@...tanamicro.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Alistair Francis <Alistair.Francis@....com>,
        KVM General <kvm@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR RISC-V (KVM/riscv)" 
        <kvm-riscv@...ts.infradead.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/7] RISC-V: KVM: Reduce KVM_MAX_VCPUS value

On Wed, May 4, 2022 at 7:45 AM Atish Patra <atishp@...shpatra.org> wrote:
>
> On Wed, Apr 20, 2022 at 4:25 AM Anup Patel <apatel@...tanamicro.com> wrote:
> >
> > Currently, the KVM_MAX_VCPUS value is 16384 for RV64 and 128
> > for RV32.
> >
> > The KVM_MAX_VCPUS value is too high for RV64 and too low for
> > RV32 compared to other architectures (e.g. x86 sets it to 1024
> > and ARM64 sets it to 512). The too high value of KVM_MAX_VCPUS
> > on RV64 also leads to VCPU mask on stack consuming 2KB.
> >
> > We set KVM_MAX_VCPUS to 1024 for both RV64 and RV32 to be
> > aligned other architectures.
> >
> > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > ---
> >  arch/riscv/include/asm/kvm_host.h | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> > index 806f74dc0bfc..61d8b40e3d82 100644
> > --- a/arch/riscv/include/asm/kvm_host.h
> > +++ b/arch/riscv/include/asm/kvm_host.h
> > @@ -16,8 +16,7 @@
> >  #include <asm/kvm_vcpu_fp.h>
> >  #include <asm/kvm_vcpu_timer.h>
> >
> > -#define KVM_MAX_VCPUS                  \
> > -       ((HGATP_VMID_MASK >> HGATP_VMID_SHIFT) + 1)
> > +#define KVM_MAX_VCPUS                  1024
> >
> >  #define KVM_HALT_POLL_NS_DEFAULT       500000
> >
> > --
> > 2.25.1
> >
>
> Reviewed-by: Atish Patra <atishp@...osinc.com>

Queued this patch for 5.19

Thanks,
Anup

>
> --
> Regards,
> Atish