linux-kernel - [RFC PATCH 2/2] RISC-V: KVM: Add support for SBI_FWFT_POINTER_MASKING

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Message-ID: <20250111004702.2813013-3-samuel.holland@sifive.com>
Date: Fri, 10 Jan 2025 16:46:59 -0800
From: Samuel Holland <samuel.holland@...ive.com>
To: Anup Patel <anup@...infault.org>,
	Atish Patra <atishp@...shpatra.org>,
	kvm-riscv@...ts.infradead.org,
	linux-riscv@...ts.infradead.org
Cc: Samuel Holland <samuel.holland@...ive.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH 2/2] RISC-V: KVM: Add support for SBI_FWFT_POINTER_MASKING_PMLEN

Pointer masking is controlled through a WARL field in henvcfg. Expose
the feature only if at least one PMLEN value is supported for VS-mode.
Allow the VMM to block access to the feature by disabling the Smnpm ISA
extension in the guest.

Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

 arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h |  2 +
 arch/riscv/kvm/vcpu_onereg.c               |  1 -
 arch/riscv/kvm/vcpu_sbi_fwft.c             | 70 +++++++++++++++++++++-
 3 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
index 5782517f6e08..5176344d9162 100644
--- a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
@@ -30,6 +30,8 @@ struct kvm_sbi_fwft_config {
 /* FWFT data structure per vcpu */
 struct kvm_sbi_fwft {
 	struct kvm_sbi_fwft_config *configs;
+	bool have_vs_pmlen_7;
+	bool have_vs_pmlen_16;
 };
 
 #define vcpu_to_fwft(vcpu) (&(vcpu)->arch.fwft_context)
diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
index 93115abca3b8..1d2033b33e6d 100644
--- a/arch/riscv/kvm/vcpu_onereg.c
+++ b/arch/riscv/kvm/vcpu_onereg.c
@@ -168,7 +168,6 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
 	case KVM_RISCV_ISA_EXT_C:
 	case KVM_RISCV_ISA_EXT_I:
 	case KVM_RISCV_ISA_EXT_M:
-	case KVM_RISCV_ISA_EXT_SMNPM:
 	/* There is not architectural config bit to disable sscofpmf completely */
 	case KVM_RISCV_ISA_EXT_SSCOFPMF:
 	case KVM_RISCV_ISA_EXT_SSNPM:
diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
index 1e85ff6666af..6e8f818fd6f5 100644
--- a/arch/riscv/kvm/vcpu_sbi_fwft.c
+++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
@@ -68,13 +68,81 @@ static int kvm_sbi_fwft_get_misaligned_delegation(struct kvm_vcpu *vcpu,
 	return SBI_SUCCESS;
 }
 
+static bool try_to_set_pmm(unsigned long value)
+{
+	csr_set(CSR_HENVCFG, value);
+	return (csr_read_clear(CSR_HENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
+}
+
+static bool kvm_sbi_fwft_pointer_masking_pmlen_supported(struct kvm_vcpu *vcpu)
+{
+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
+
+	if (!riscv_isa_extension_available(vcpu->arch.isa, SMNPM))
+		return false;
+
+	fwft->have_vs_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
+	fwft->have_vs_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
+
+	return fwft->have_vs_pmlen_7 || fwft->have_vs_pmlen_16;
+}
+
+static int kvm_sbi_fwft_set_pointer_masking_pmlen(struct kvm_vcpu *vcpu,
+						  struct kvm_sbi_fwft_config *conf,
+						  unsigned long value)
+{
+	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
+	unsigned long pmm;
+
+	if (value == 0)
+		pmm = ENVCFG_PMM_PMLEN_0;
+	else if (value <= 7 && fwft->have_vs_pmlen_7)
+		pmm = ENVCFG_PMM_PMLEN_7;
+	else if (value <= 16 && fwft->have_vs_pmlen_16)
+		pmm = ENVCFG_PMM_PMLEN_16;
+	else
+		return SBI_ERR_INVALID_PARAM;
+
+	vcpu->arch.cfg.henvcfg &= ~ENVCFG_PMM;
+	vcpu->arch.cfg.henvcfg |= pmm;
+
+	return SBI_SUCCESS;
+}
+
+static int kvm_sbi_fwft_get_pointer_masking_pmlen(struct kvm_vcpu *vcpu,
+						  struct kvm_sbi_fwft_config *conf,
+						  unsigned long *value)
+{
+	switch (vcpu->arch.cfg.henvcfg & ENVCFG_PMM) {
+	case ENVCFG_PMM_PMLEN_0:
+		*value = 0;
+		break;
+	case ENVCFG_PMM_PMLEN_7:
+		*value = 7;
+		break;
+	case ENVCFG_PMM_PMLEN_16:
+		*value = 16;
+		break;
+	default:
+		return SBI_ERR_FAILURE;
+	}
+
+	return SBI_SUCCESS;
+}
+
 static const struct kvm_sbi_fwft_feature features[] = {
 	{
 		.id = SBI_FWFT_MISALIGNED_EXC_DELEG,
 		.supported = kvm_sbi_fwft_misaligned_delegation_supported,
 		.set = kvm_sbi_fwft_set_misaligned_delegation,
 		.get = kvm_sbi_fwft_get_misaligned_delegation,
-	}
+	},
+	{
+		.id = SBI_FWFT_POINTER_MASKING_PMLEN,
+		.supported = kvm_sbi_fwft_pointer_masking_pmlen_supported,
+		.set = kvm_sbi_fwft_set_pointer_masking_pmlen,
+		.get = kvm_sbi_fwft_get_pointer_masking_pmlen,
+	},
 };
 
 static struct kvm_sbi_fwft_config *
-- 
2.47.0