linux-kernel - [PATCH] RISC-V: KVM: Fix SBI_FWFT_POINTER_MASKING

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Message-ID: <20250915053431.1910941-1-samuel.holland@sifive.com>
Date: Sun, 14 Sep 2025 22:34:20 -0700
From: Samuel Holland <samuel.holland@...ive.com>
To: Anup Patel <anup@...infault.org>,
	Atish Patra <atish.patra@...ux.dev>,
	kvm-riscv@...ts.infradead.org
Cc: Samuel Holland <samuel.holland@...ive.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Alexandre Ghiti <alex@...ti.fr>,
	Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org
Subject: [PATCH] RISC-V: KVM: Fix SBI_FWFT_POINTER_MASKING_PMLEN algorithm

The implementation of SBI_FWFT_POINTER_MASKING_PMLEN from commit
aa04d131b88b ("RISC-V: KVM: Add support for SBI_FWFT_POINTER_MASKING_PMLEN")
was based on a draft of the SBI 3.0 specification, and is not compliant
with the ratified version.

Update the algorithm to be compliant. Specifically, do not fall back to
a pointer masking mode with a larger PMLEN if the mode with the
requested PMLEN is unsupported by the hardware.

Fixes: aa04d131b88b ("RISC-V: KVM: Add support for SBI_FWFT_POINTER_MASKING_PMLEN")
Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---
I saw that the RFC version of this patch already made it into
riscv_kvm_queue, but it needs an update for ratified SBI 3.0. Feel free
to squash this into the original commit, or I can send a replacement v2
patch if you prefer.

 arch/riscv/kvm/vcpu_sbi_fwft.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
index cacb3d4410a54..62cc9c3d57599 100644
--- a/arch/riscv/kvm/vcpu_sbi_fwft.c
+++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
@@ -160,14 +160,23 @@ static long kvm_sbi_fwft_set_pointer_masking_pmlen(struct kvm_vcpu *vcpu,
 	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
 	unsigned long pmm;
 
-	if (value == 0)
+	switch (value) {
+	case 0:
 		pmm = ENVCFG_PMM_PMLEN_0;
-	else if (value <= 7 && fwft->have_vs_pmlen_7)
+		break;
+	case 7:
+		if (!fwft->have_vs_pmlen_7)
+			return SBI_ERR_INVALID_PARAM;
 		pmm = ENVCFG_PMM_PMLEN_7;
-	else if (value <= 16 && fwft->have_vs_pmlen_16)
+		break;
+	case 16:
+		if (!fwft->have_vs_pmlen_16)
+			return SBI_ERR_INVALID_PARAM;
 		pmm = ENVCFG_PMM_PMLEN_16;
-	else
+		break;
+	default:
 		return SBI_ERR_INVALID_PARAM;
+	}
 
 	vcpu->arch.cfg.henvcfg &= ~ENVCFG_PMM;
 	vcpu->arch.cfg.henvcfg |= pmm;
-- 
2.47.2

base-commit: 7835b892d1d9f52fb61537757aa446fb44984215
branch: up/kvm-fwft-pmlen