linux-kernel - [PATCH 6.6 3/8] KVM: arm64: Remove host FPSIMD saving for non-protected KVM

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Message-Id: <20250321-stable-sve-6-6-v1-3-0b3a6a14ea53@kernel.org>
Date: Fri, 21 Mar 2025 00:16:03 +0000
From: Mark Brown <broonie@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 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>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Fuad Tabba <tabba@...gle.com>
Subject: [PATCH 6.6 3/8] KVM: arm64: Remove host FPSIMD saving for
 non-protected KVM

From: Mark Rutland <mark.rutland@....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@....com>
Reviewed-by: Mark Brown <broonie@...nel.org>
Tested-by: Mark Brown <broonie@...nel.org>
Acked-by: Will Deacon <will@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Fuad Tabba <tabba@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>
Cc: Oliver Upton <oliver.upton@...ux.dev>
Reviewed-by: Oliver Upton <oliver.upton@...ux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-3-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@...nel.org>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/include/asm/kvm_host.h       | 1 -
 arch/arm64/kvm/fpsimd.c                 | 2 --
 arch/arm64/kvm/hyp/include/hyp/switch.h | 4 ----
 arch/arm64/kvm/hyp/nvhe/hyp-main.c      | 1 -
 4 files changed, 8 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 6a165ec5d3b74ece3e98e7bf45f3ea94cc30e6ec..3891963d42e00c8f999886dc5d7322bbacbc6c7f 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -535,7 +535,6 @@ 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 {
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 8b55de502c8c220e15e3a6b782d5012b9349b612..7c36d2a7aa3196056f76acfe8f9c41763ed67d9d 100644
--- 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_vcpu *vcpu)
 	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
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 9cfe6bd1dbe459cb3588bccd94359369a546947e..1cdc8d161e7dd3aeeb6b03170e239b0c1ace7790 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -321,10 +321,6 @@ static bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
 	}
 	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);
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 67cc07283e642ab07e1c98c5745e2c6a2dd4f36e..8390173f7f5b38e01c04ae6563853df11a1c3df2 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -41,7 +41,6 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 	hyp_vcpu->vcpu.arch.fp_state	= host_vcpu->arch.fp_state;
 
 	hyp_vcpu->vcpu.arch.debug_ptr	= kern_hyp_va(host_vcpu->arch.debug_ptr);
-	hyp_vcpu->vcpu.arch.host_fpsimd_state = host_vcpu->arch.host_fpsimd_state;
 
 	hyp_vcpu->vcpu.arch.vsesr_el2	= host_vcpu->arch.vsesr_el2;
 

-- 
2.39.5