linux-kernel - [PATCH v4 3/4] KVM: arm64: Fix FFR offset calculation for pKVM host state save and restore

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Message-Id: <20240704-kvm-arm64-fix-pkvm-sve-vl-v4-3-b6898ab23dc4@kernel.org>
Date: Thu, 04 Jul 2024 18:28:18 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, 
 Oliver Upton <oliver.upton@...ux.dev>, James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, Fuad Tabba <tabba@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 kvmarm@...ts.linux.dev, Mark Brown <broonie@...nel.org>
Subject: [PATCH v4 3/4] KVM: arm64: Fix FFR offset calculation for pKVM
 host state save and restore

When saving and restoring the SVE state for the host we configure the
hardware for the maximum VL it supports, but when calculating offsets in
memory we use the maximum usable VL for the host. Since these two values
may not be the same this may result in data corruption.  We can just
read the current VL from the hardware with an instruction so do that
instead of a saved value, we need to correct the value and this makes
the consistency obvious.

Fixes: b5b9955617bc ("KVM: arm64: Eagerly restore host fpsimd/sve state in pKVM")
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/include/asm/kvm_hyp.h        | 1 +
 arch/arm64/kvm/hyp/fpsimd.S             | 5 +++++
 arch/arm64/kvm/hyp/include/hyp/switch.h | 2 +-
 arch/arm64/kvm/hyp/nvhe/hyp-main.c      | 2 +-
 4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index b05bceca3385..7510383d78a6 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -113,6 +113,7 @@ void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
 void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
 void __sve_save_state(void *sve_pffr, u32 *fpsr, int save_ffr);
 void __sve_restore_state(void *sve_pffr, u32 *fpsr, int restore_ffr);
+int __sve_get_vl(void);
 
 u64 __guest_enter(struct kvm_vcpu *vcpu);
 
diff --git a/arch/arm64/kvm/hyp/fpsimd.S b/arch/arm64/kvm/hyp/fpsimd.S
index e950875e31ce..d272dbf36da8 100644
--- a/arch/arm64/kvm/hyp/fpsimd.S
+++ b/arch/arm64/kvm/hyp/fpsimd.S
@@ -31,3 +31,8 @@ SYM_FUNC_START(__sve_save_state)
 	sve_save 0, x1, x2, 3
 	ret
 SYM_FUNC_END(__sve_save_state)
+
+SYM_FUNC_START(__sve_get_vl)
+	_sve_rdvl	0, 1
+	ret
+SYM_FUNC_END(__sve_get_vl)
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 0c4de44534b7..06efcca765cc 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -327,7 +327,7 @@ static inline void __hyp_sve_save_host(void)
 
 	sve_state->zcr_el1 = read_sysreg_el1(SYS_ZCR);
 	write_sysreg_s(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
-	__sve_save_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
+	__sve_save_state(sve_state->sve_regs + sve_ffr_offset(__sve_get_vl()),
 			 &sve_state->fpsr,
 			 true);
 }
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index f43d845f3c4e..bd8f671e848c 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -49,7 +49,7 @@ static void __hyp_sve_restore_host(void)
 	 * supported by the system (or limited at EL3).
 	 */
 	write_sysreg_s(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
-	__sve_restore_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
+	__sve_restore_state(sve_state->sve_regs + sve_ffr_offset(__sve_get_vl()),
 			    &sve_state->fpsr,
 			    true);
 	write_sysreg_el1(sve_state->zcr_el1, SYS_ZCR);

-- 
2.39.2