linux-kernel - [PATCH v3 10/14] RISC-V: KVM: Disable all hpmcounter access for VS/VU mode

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Message-Id: <20230127182558.2416400-11-atishp@rivosinc.com>
Date:   Fri, 27 Jan 2023 10:25:54 -0800
From:   Atish Patra <atishp@...osinc.com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atishp@...osinc.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Guo Ren <guoren@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
        kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Sergey Matyukevich <sergey.matyukevich@...tacore.com>,
        Will Deacon <will@...nel.org>
Subject: [PATCH v3 10/14] RISC-V: KVM: Disable all hpmcounter access for VS/VU mode

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 hcounteren.

However, instret and cycle access for guest user space 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 interface is not settled yet.

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
Signed-off-by: Atish Patra <atishp@...osinc.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..c5d400f 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 the time counter directly. Everything else should trap */
+	csr_write(CSR_HCOUNTEREN, 0x02);
 
 	csr_write(CSR_HVIP, 0);
 
-- 
2.25.1