linux-kernel - Re: [PATCH v3] RISC-V: KVM: Remove scounteren initialization

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Message-ID: <C74B29B0-FB1F-4E67-AFDF-FAD7C86FB329@ventanamicro.com>
Date: Fri, 16 May 2025 11:56:31 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: kvm-riscv@...ts.infradead.org, Atish Patra <atishp@...osinc.com>,
 Anup Patel <anup@...infault.org>, Atish Patra <atishp@...shpatra.org>,
 Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Alexandre Ghiti <alex@...ti.fr>
CC: kvm@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] RISC-V: KVM: Remove scounteren initialization

On May 16, 2025 1:11:18 AM GMT+02:00, Atish Patra <atishp@...osinc.com> wrote:
>Scounteren CSR controls the direct access the hpmcounters and cycle/
>instret/time from the userspace. It's the supervisor's responsibility
>to set it up correctly for it's user space. They hypervisor doesn't
>need to decide the policy on behalf of the supervisor.
>
>Signed-off-by: Atish Patra <atishp@...osinc.com>
>---
>Changes in v3:
>- Removed the redundant declaration 
>- Link to v2: https://lore.kernel.org/r/20250515-fix_scounteren_vs-v2-1-1fd8dc0693e8@rivosinc.com
>
>Changes in v2:
>- Remove the scounteren initialization instead of just setting the TM bit. 
>- Link to v1: https://lore.kernel.org/r/20250513-fix_scounteren_vs-v1-1-c1f52af93c79@rivosinc.com
>---
> arch/riscv/kvm/vcpu.c | 4 ----
> 1 file changed, 4 deletions(-)
>
>diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
>index 60d684c76c58..9bfaae9a11ea 100644
>--- a/arch/riscv/kvm/vcpu.c
>+++ b/arch/riscv/kvm/vcpu.c
>@@ -111,7 +111,6 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> {
> 	int rc;
> 	struct kvm_cpu_context *cntx;
>-	struct kvm_vcpu_csr *reset_csr = &vcpu->arch.guest_reset_csr;
> 
> 	spin_lock_init(&vcpu->arch.mp_state_lock);
> 
>@@ -146,9 +145,6 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> 	if (kvm_riscv_vcpu_alloc_vector_context(vcpu, cntx))
> 		return -ENOMEM;
> 
>-	/* By default, make CY, TM, and IR counters accessible in VU mode */
>-	reset_csr->scounteren = 0x7;
>-
> 	/* Setup VCPU timer */
> 	kvm_riscv_vcpu_timer_init(vcpu);
> 
>
>---
>base-commit: 01f95500a162fca88cefab9ed64ceded5afabc12
>change-id: 20250513-fix_scounteren_vs-fdd86255c7b7
>--
>Regards,
>Atish patra
>
>

Signed-off-by: Andrew Jones <ajones@...tanamicro.com>