On Thu, May 15, 2025 at 2:31 AM Atish Kumar Patra <atishp@xxxxxxxxxxxx> wrote: > > On Wed, May 14, 2025 at 3:55 AM Anup Patel <anup@xxxxxxxxxxxxxx> wrote: > > > > On Wed, May 14, 2025 at 12:13 PM Atish Patra <atishp@xxxxxxxxxxxx> wrote: > > > > > > The KVM virtualizes PMU in RISC-V and disables all counter access except > > > TM bit by default vi hstateen CSR. There is no benefit in enabling CY/TM > > > bits in scounteren for the guest user space as it can't be run without > > > hcounteren anyways. > > > > > > Allow only TM bit which matches the hcounteren default setting. > > > > > > Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx> > > > --- > > > arch/riscv/kvm/vcpu.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c > > > index 60d684c76c58..873593bfe610 100644 > > > --- a/arch/riscv/kvm/vcpu.c > > > +++ b/arch/riscv/kvm/vcpu.c > > > @@ -146,8 +146,8 @@ 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; > > > + /* By default, only TM should be accessible in VU mode */ > > > + reset_csr->scounteren = 0x2; > > > > Let's remove this as well because the Linux SBI PMU driver > > does initialize scounteren correctly. > > > > But other guests may not. I thought time should be a basic one that > should be allowed by default. > There is no specification (SBI or Priv spec) which mandates M-mode or HS-mode to setup S-mode CSRs. Setting scounteren bits (including TM bit) has always been a HACK or work-around. It is better to remove scounteren initialization HACK from KVM RISC-V before more supervisor software starts depending on it. Regards, Anup
