linux-kernel - [PATCH 5.15 v2 05/10] arm64/fpsimd: Stop using TIF

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Message-Id: <20250403-stable-sve-5-15-v2-5-30a36a78a20a@kernel.org>
Date: Thu, 03 Apr 2025 00:20:20 +0100
From: Mark Brown <broonie@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
 Oleg Nesterov <oleg@...hat.com>, Oliver Upton <oliver.upton@...ux.dev>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>, Mark Rutland <mark.rutland@....com>
Subject: [PATCH 5.15 v2 05/10] 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 | 40 ++++++++++++++++------------------------
 arch/arm64/kvm/fpsimd.c    |  3 ---
 2 files changed, 16 insertions(+), 27 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 105b8aa0c038..e8f10daaa0d7 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -318,7 +318,13 @@ static void task_fpsimd_load(void)
 
 /*
  * Ensure FPSIMD/SVE storage in memory for the loaded context is up to
- * date with respect to the CPU registers.
+ * date with respect to the CPU registers. Note carefully that the
+ * current context is the context last bound to the CPU stored in
+ * 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, 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)
 {
@@ -334,9 +340,15 @@ static void fpsimd_save(void)
 	if (test_thread_flag(TIF_FOREIGN_FPSTATE))
 		return;
 
-	if (IS_ENABLED(CONFIG_ARM64_SVE) &&
-	    test_thread_flag(TIF_SVE)) {
-		if (WARN_ON(sve_get_vl() != last->sve_vl)) {
+	if ((last->to_save == FP_STATE_CURRENT && test_thread_flag(TIF_SVE)) ||
+	    last->to_save == FP_STATE_SVE) {
+		save_sve_regs = true;
+		vl = last->sve_vl;
+	}
+
+	if (IS_ENABLED(CONFIG_ARM64_SVE) && save_sve_regs) {
+		/* Get the configured VL from RDVL, will account for SM */
+		if (WARN_ON(sve_get_vl() != vl)) {
 			/*
 			 * Can't save the user regs, so current would
 			 * re-enter user with corrupt state.
@@ -347,26 +359,6 @@ static void fpsimd_save(void)
 		}
 	}
 
-	if (test_thread_flag(TIF_SVE)) {
-		save_sve_regs = 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 (IS_ENABLED(CONFIG_ARM64_SVE) && save_sve_regs) {
 		sve_save_state((char *)last->sve_state +
 			       sve_ffr_offset(last->sve_vl),
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 54a31c97eb7a..2e0f44f4c470 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -110,7 +110,6 @@ 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));
 	}
 }
 
@@ -151,7 +150,5 @@ 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