linux-kernel - [PATCH 6.1 04/12] arm64/fpsimd: Stop using TIF

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Message-Id: <20250325-stable-sve-6-1-v1-4-83259d427d84@kernel.org>
Date: Tue, 25 Mar 2025 18:48:18 +0000
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, 
 James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, 
 Oliver Upton <oliver.upton@...ux.dev>, Oleg Nesterov <oleg@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 kvmarm@...ts.linux.dev, kvmarm@...ts.cs.columbia.edu, 
 Mark Brown <broonie@...nel.org>, Mark Rutland <mark.rutland@....com>
Subject: [PATCH 6.1 04/12] arm64/fpsimd: Stop using TIF_SVE to manage
 register saving in KVM

[ Upstream commit 62021cc36add7b2c015b837f7893f2fb4b8c2586 ]

Now that we are explicitly telling the host FP code which register state
it needs to save we can remove the manipulation of TIF_SVE from the KVM
code, simplifying it and allowing us to optimise our handling of normal
tasks. Remove the manipulation of TIF_SVE from KVM and instead rely on
to_save to ensure we save the correct data for it.

There should be no functional or performance impact from this change.

Signed-off-by: Mark Brown <broonie@...nel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Reviewed-by: Marc Zyngier <maz@...nel.org>
Link: https://lore.kernel.org/r/20221115094640.112848-5-broonie@kernel.org
Signed-off-by: Will Deacon <will@...nel.org>
[ Mark: trivial backport ]
Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/kernel/fpsimd.c | 22 ++++------------------
 arch/arm64/kvm/fpsimd.c    |  3 ---
 2 files changed, 4 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 1f6fd9229e536966292a9751f08103912a48ba07..3fcacbce5d427e274a9439b8a6f9edf4080d54a4 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -439,8 +439,8 @@ static void task_fpsimd_load(void)
  * last, if KVM is involved this may be the guest VM context rather
  * than the host thread for the VM pointed to by current. This means
  * that we must always reference the state storage via last rather
- * than via current, other than the TIF_ flags which KVM will
- * carefully maintain for us.
+ * than via current, if we are saving KVM state then it will have
+ * ensured that the type of registers to save is set in last->to_save.
  */
 static void fpsimd_save(void)
 {
@@ -457,27 +457,13 @@ static void fpsimd_save(void)
 	if (test_thread_flag(TIF_FOREIGN_FPSTATE))
 		return;
 
-	if (test_thread_flag(TIF_SVE)) {
+	if ((last->to_save == FP_STATE_CURRENT && test_thread_flag(TIF_SVE)) ||
+	    last->to_save == FP_STATE_SVE) {
 		save_sve_regs = true;
 		save_ffr = true;
 		vl = last->sve_vl;
 	}
 
-	/*
-	 * Validate that an explicitly specified state to save is
-	 * consistent with the task state.
-	 */
-	switch (last->to_save) {
-	case FP_STATE_CURRENT:
-		break;
-	case FP_STATE_FPSIMD:
-		WARN_ON_ONCE(save_sve_regs);
-		break;
-	case FP_STATE_SVE:
-		WARN_ON_ONCE(!save_sve_regs);
-		break;
-	}
-
 	if (system_supports_sme()) {
 		u64 *svcr = last->svcr;
 
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 89c02ce797b874196eff978464a936dfb020ad02..ec82d0191f76717ad17a43f87bd8a806eb4ab3b8 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -151,7 +151,6 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
 					 &vcpu->arch.fp_type, fp_type);
 
 		clear_thread_flag(TIF_FOREIGN_FPSTATE);
-		update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
 	}
 }
 
@@ -208,7 +207,5 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
 			sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
 	}
 
-	update_thread_flag(TIF_SVE, 0);
-
 	local_irq_restore(flags);
 }

-- 
2.39.5