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

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Date:   Tue, 3 May 2022 19:15:20 -0700
From:   Atish Patra <atishp@...shpatra.org>
To:     Anup Patel <apatel@...tanamicro.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Alistair Francis <Alistair.Francis@....com>,
        Anup Patel <anup@...infault.org>,
        KVM General <kvm@...r.kernel.org>,
        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, 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>

-- 
Regards,
Atish