linux-kernel - [PATCH 07/10] KVM: arm64: Remove host FPSIMD saving for non-protected KVM

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Message-Id: <20250402-stable-sve-5-15-v1-7-84d0e5ff1102@kernel.org>
Date: Wed, 02 Apr 2025 23:59:39 +0100
From: Mark Brown <broonie@...nel.org>
To: 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, Mark Brown <broonie@...nel.org>, 
 Mark Rutland <mark.rutland@....com>, Fuad Tabba <tabba@...gle.com>
Subject: [PATCH 07/10] 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                 | 1 -
 arch/arm64/kvm/hyp/include/hyp/switch.h | 6 +-----
 3 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index ecae31b0dab3..06e8d4645ecd 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -333,7 +333,6 @@ struct kvm_vcpu_arch {
 	struct kvm_guest_debug_arch external_debug_state;
 
 	struct thread_info *host_thread_info;	/* hyp VA */
-	struct user_fpsimd_state *host_fpsimd_state;	/* hyp VA */
 
 	struct {
 		/* {Break,watch}point registers */
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 2afa2521bce1..1ef9d6cb91ee 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -55,7 +55,6 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
 	}
 
 	vcpu->arch.host_thread_info = kern_hyp_va(ti);
-	vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
 error:
 	return ret;
 }
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 269ec3587210..cc102e46b0e2 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -251,11 +251,7 @@ static inline bool __hyp_handle_fpsimd(struct kvm_vcpu *vcpu)
 	}
 	isb();
 
-	if (vcpu->arch.flags & KVM_ARM64_FP_HOST) {
-		__fpsimd_save_state(vcpu->arch.host_fpsimd_state);
-		vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
-	}
-
+	/* Restore the guest state */
 	if (sve_guest)
 		__hyp_sve_restore_guest(vcpu);
 	else

-- 
2.39.5