From 9bcbb6104a344d3526e185ee1e7b985509914e90 Mon Sep 17 00:00:00 2001
From: Lokesh Vutla <lokeshvutla@google.com>
Date: Tue, 21 Jan 2025 04:40:16 +0000
Subject: [PATCH] KVM: arm64: Flush hyp bss section after initialization of
variables in bss
To determine CPU features during initialization, the nVHE hypervisor
utilizes sanitized values of the host's CPU features registers. These
values, stored in u64 idaa64*_el1_sys_val variables are updated by the
kvm_hyp_init_symbols() function at EL1. To ensure EL2 visibility with
the MMU off, the data cache needs to be flushed after these updates.
However, individually flushing each variable using
kvm_flush_dcache_to_poc() is inefficient.
These cpu feature variables would be part of the bss section of
the hypervisor. Hence, flush the entire bss section of hypervisor
once the initialization is complete.
Fixes: 6c30bfb18d0b ("KVM: arm64: Add handlers for protected VM System Registers")
Suggested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@google.com>
Link: https://lore.kernel.org/r/20250121044016.2219256-1-lokeshvutla@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/arm.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index bcc4f7e92634..0725a0b50a3e 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2400,6 +2400,13 @@ static void kvm_hyp_init_symbols(void)
kvm_nvhe_sym(id_aa64smfr0_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64SMFR0_EL1);
kvm_nvhe_sym(__icache_flags) = __icache_flags;
kvm_nvhe_sym(kvm_arm_vmid_bits) = kvm_arm_vmid_bits;
+
+ /*
+ * Flush entire BSS since part of its data containing init symbols is read
+ * while the MMU is off.
+ */
+ kvm_flush_dcache_to_poc(kvm_ksym_ref(__hyp_bss_start),
+ kvm_ksym_ref(__hyp_bss_end) - kvm_ksym_ref(__hyp_bss_start));
}
static int __init kvm_hyp_init_protection(u32 hyp_va_bits)