linux-kernel - [PATCH RFC v2 12/22] KVM: arm64: Make SVCR a normal system register

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Message-Id: <20231222-kvm-arm64-sme-v2-12-da226cb180bb@kernel.org>
Date: Fri, 22 Dec 2023 16:21:20 +0000
From: Mark Brown <broonie@...nel.org>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
 James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
 Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, 
 Shuah Khan <shuah@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
 linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>
Subject: [PATCH RFC v2 12/22] KVM: arm64: Make SVCR a normal system
 register

As a placeholder while SME guests were not supported we provide a u64 in
struct kvm_vcpu_arch for the host kernel's floating point save code to use
when managing KVM guests. In order to support KVM guests we will need to
replace this with a proper KVM system register, do so and update the system
register definition to make it accessible to the guest if it has SME.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/include/asm/kvm_host.h | 2 +-
 arch/arm64/kvm/fpsimd.c           | 8 +++++---
 arch/arm64/kvm/sys_regs.c         | 2 +-
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 36bf9d7e92e1..690c439b5e2a 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -356,6 +356,7 @@ enum vcpu_sysreg {
 	MDCCINT_EL1,	/* Monitor Debug Comms Channel Interrupt Enable Reg */
 	OSLSR_EL1,	/* OS Lock Status Register */
 	DISR_EL1,	/* Deferred Interrupt Status Register */
+	SVCR,		/* Scalable Vector Control Register */
 
 	/* Performance Monitors Registers */
 	PMCR_EL0,	/* Control Register */
@@ -518,7 +519,6 @@ struct kvm_vcpu_arch {
 	void *sve_state;
 	enum fp_type fp_type;
 	unsigned int max_vl[ARM64_VEC_MAX];
-	u64 svcr;
 
 	/* Stage 2 paging state used by the hardware on next switch */
 	struct kvm_s2_mmu *hw_mmu;
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index a402a072786a..1be18d719fce 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -145,14 +145,16 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
 	if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
 
 		/*
-		 * Currently we do not support SME guests so SVCR is
-		 * always 0 and we just need a variable to point to.
+		 * We peer into the registers since SVCR is saved as
+		 * part of the floating point state, determining which
+		 * registers exist and their size, so is saved by
+		 * fpsimd_save().
 		 */
 		fp_state.st = &vcpu->arch.ctxt.fp_regs;
 		fp_state.sve_state = vcpu->arch.sve_state;
 		fp_state.sve_vl = vcpu->arch.max_vl[ARM64_VEC_SVE];
 		fp_state.sme_state = NULL;
-		fp_state.svcr = &vcpu->arch.svcr;
+		fp_state.svcr = &(vcpu->arch.ctxt.sys_regs[SVCR]);
 		fp_state.fp_type = &vcpu->arch.fp_type;
 
 		if (vcpu_has_sve(vcpu))
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index b618bcab526e..f908aa3fb606 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2336,7 +2336,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	  .get_user = get_id_reg, .visibility = sme_visibility },
 	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
 	{ SYS_DESC(SYS_CTR_EL0), access_ctr },
-	{ SYS_DESC(SYS_SVCR), undef_access },
+	{ SYS_DESC(SYS_SVCR), NULL, reset_val, SVCR, 0, .visibility = sme_visibility },
 
 	{ PMU_SYS_REG(PMCR_EL0), .access = access_pmcr, .reset = reset_pmcr,
 	  .reg = PMCR_EL0, .get_user = get_pmcr, .set_user = set_pmcr },

-- 
2.30.2