[PATCH v3 1/3] KVM: arm64: Synchronise kvm_host_data before host deprivileging

[Fuad Tabba <fuad.tabba@linux.dev>]

From: Vincent Donnefort <vdonnefort@google.com>

When protected mode is enabled, the host is populating and reading the
hypervisor copy of kvm_host_data until it is deprivileged. This is an
issue for nr_event_counters which is only used by the host to populate
mdcr_el2. After deprivileging, it is reading an uninitialised value and
sets HPMN to 0, preventing programmable event counters from counting a
non-protected guest.

Before the host is entirely deprivileged, copy the entire kvm_host_data
content from the hypervisor copy to the host-accessible one.

Fixes: 2417218f2f23 ("KVM: arm64: Get rid of __kvm_get_mdcr_el2() and related warts")
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kvm/pkvm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index 380dfb1db0be4..58190ff6723d6 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -316,6 +316,12 @@ static void __init _kvm_host_prot_finalize(void *arg)
 {
 	int *err = arg;
 
+	/*
+	 * After __pkvm_prot_finalize, access to the hypervisor copy of
+	 * kvm_host_data is lost. Save it into the host-accessible version.
+	 */
+	*this_cpu_ptr(&kvm_host_data) = *this_cpu_ptr_nvhe_sym(kvm_host_data);
+
 	if (WARN_ON(kvm_call_hyp_nvhe(__pkvm_prot_finalize)))
 		WRITE_ONCE(*err, -EINVAL);
 }
-- 
2.47.3