[PATCH v2 08/11] RISC-V: KVM: Disable all hpmcounter access for VS/VU mode

[Atish Patra <atishp@rivosinc.com>]

Any guest must not get access to any hpmcounter including cycle/instret
without any checks. We achieve that by disabling all the bits except TM
bit in hcountern.

However, instret and cycle access for guest userspace can be enabled
upon explicit request (via ONE REG) or on first trap from VU mode
to maintain ABI requirement in the future. This patch doesn't support
that as ONE REG inteface is not settled yet.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 arch/riscv/kvm/main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
index 58c5489..9c2efd3 100644
--- a/arch/riscv/kvm/main.c
+++ b/arch/riscv/kvm/main.c
@@ -49,7 +49,8 @@ int kvm_arch_hardware_enable(void)
 	hideleg |= (1UL << IRQ_VS_EXT);
 	csr_write(CSR_HIDELEG, hideleg);
 
-	csr_write(CSR_HCOUNTEREN, -1UL);
+	/* VS should access only TM bit. Everything else should trap */
+	csr_write(CSR_HCOUNTEREN, 0x02);
 
 	csr_write(CSR_HVIP, 0);
 
-- 
2.25.1