releases/6.1.135/kvm-arm64-remove-host-fpsimd-saving-for-non-protected-kvm.patch

From broonie@kernel.org Fri Apr  4 15:27:48 2025
From: Mark Brown <broonie@kernel.org>
Date: Fri, 04 Apr 2025 14:23:39 +0100
Subject: KVM: arm64: Remove host FPSIMD saving for non-protected KVM
To: Catalin Marinas <catalin.marinas@arm.com>,  Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,  James Morse <james.morse@arm.com>,  Suzuki K Poulose <suzuki.poulose@arm.com>,  Oliver Upton <oliver.upton@linux.dev>, Oleg Nesterov <oleg@redhat.com>,  Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,  kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,  Mark Brown <broonie@kernel.org>, stable@vger.kernel.org,  Mark Rutland <mark.rutland@arm.com>, Fuad Tabba <tabba@google.com>
Message-ID: <20250404-stable-sve-6-1-v1-6-cd5c9eb52d49@kernel.org>

From: Mark Rutland <mark.rutland@arm.com>

[ Upstream commit 8eca7f6d5100b6997df4f532090bc3f7e0203bef ]

Now that the host eagerly saves its own FPSIMD/SVE/SME state,
non-protected KVM never needs to save the host FPSIMD/SVE/SME state,
and the code to do this is never used. Protected KVM still needs to
save/restore the host FPSIMD/SVE state to avoid leaking guest state to
the host (and to avoid revealing to the host whether the guest used
FPSIMD/SVE/SME), and that code needs to be retained.

Remove the unused code and data structures.

To avoid the need for a stub copy of kvm_hyp_save_fpsimd_host() in the
VHE hyp code, the nVHE/hVHE version is moved into the shared switch
header, where it is only invoked when KVM is in protected mode.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-3-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm64/include/asm/kvm_host.h       |    1 -
 arch/arm64/kvm/fpsimd.c                 |    2 --
 arch/arm64/kvm/hyp/include/hyp/switch.h |    4 ----
 3 files changed, 7 deletions(-)

--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -380,7 +380,6 @@ struct kvm_vcpu_arch {
 	struct kvm_guest_debug_arch vcpu_debug_state;
 	struct kvm_guest_debug_arch external_debug_state;
 
-	struct user_fpsimd_state *host_fpsimd_state;	/* hyp VA */
 	struct task_struct *parent_task;
 
 	struct {
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -49,8 +49,6 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_
 	if (ret)
 		return ret;
 
-	vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
-
 	/*
 	 * We need to keep current's task_struct pinned until its data has been
 	 * unshared with the hypervisor to make sure it is not re-used by the
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -207,10 +207,6 @@ static bool kvm_hyp_handle_fpsimd(struct
 	}
 	isb();
 
-	/* Write out the host state if it's in the registers */
-	if (vcpu->arch.fp_state == FP_STATE_HOST_OWNED)
-		__fpsimd_save_state(vcpu->arch.host_fpsimd_state);
-
 	/* Restore the guest state */
 	if (sve_guest)
 		__hyp_sve_restore_guest(vcpu);