linux-kernel - [PATCH v6 3/8] RISC-V: KVM: Make PMU functionality depend on Sscofpmf

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Message-Id: <20230207095529.1787260-4-atishp@rivosinc.com>
Date:   Tue,  7 Feb 2023 01:55:24 -0800
From:   Atish Patra <atishp@...osinc.com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atishp@...osinc.com>,
        Anup Patel <anup@...infault.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Atish Patra <atishp@...shpatra.org>,
        kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: [PATCH v6 3/8] RISC-V: KVM: Make PMU functionality depend on Sscofpmf

The privilege mode filtering feature must be available in the host so
that the host can inhibit the counters while the execution is in HS mode.
Otherwise, the guests may have access to critical guest information.

Reviewed-by: Anup Patel <anup@...infault.org>
Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
Signed-off-by: Atish Patra <atishp@...osinc.com>
---
 arch/riscv/kvm/vcpu_pmu.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
index e79721b..6c1f073 100644
--- a/arch/riscv/kvm/vcpu_pmu.c
+++ b/arch/riscv/kvm/vcpu_pmu.c
@@ -79,6 +79,14 @@ void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
 	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
 	struct kvm_pmc *pmc;
 
+	/*
+	 * PMU functionality should be only available to guests if privilege mode
+	 * filtering is available in the host. Otherwise, guest will always count
+	 * events while the execution is in hypervisor mode.
+	 */
+	if (!riscv_isa_extension_available(NULL, SSCOFPMF))
+		return;
+
 	ret = riscv_pmu_get_hpm_info(&hpm_width, &num_hw_ctrs);
 	if (ret < 0 || !hpm_width || !num_hw_ctrs)
 		return;
-- 
2.25.1