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Subject[PATCH 2/6] KVM: nVMX: stop abusing need_vmcs12_to_shadow_sync for eVMCS mapping
Date
When vmx_set_nested_state() happens, we may not have all the required
data to map enlightened VMCS: e.g. HV_X64_MSR_VP_ASSIST_PAGE MSR may not
yet be restored so we need a postponed action. Currently, we (ab)use
need_vmcs12_to_shadow_sync/nested_sync_vmcs12_to_shadow() for that but
this is not ideal:
- We may not need to sync anything if L2 is running
- It is hard to propagate errors from nested_sync_vmcs12_to_shadow()
as we call it from vmx_prepare_switch_to_guest() which happens just
before we do VMLAUNCH, the code is not ready to handle errors there.

Move eVMCS mapping to nested_get_vmcs12_pages() and request
KVM_REQ_GET_VMCS12_PAGES, it seems to be is less abusive in nature.
It would probably be possible to introduce a specialized KVM_REQ_EVMCS_MAP
but it is undesirable to propagate eVMCS specifics all the way up to x86.c

Note, we don't need to request KVM_REQ_GET_VMCS12_PAGES from
vmx_set_nested_state() directly as nested_vmx_enter_non_root_mode() already
does that. Requesting KVM_REQ_GET_VMCS12_PAGES is done to document the
(non-obvious) side-effect and to be future proof.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/vmx/nested.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 9750e590c89d..72398e3bc92b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1997,14 +1997,6 @@ void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

- /*
- * hv_evmcs may end up being not mapped after migration (when
- * L2 was running), map it here to make sure vmcs12 changes are
- * properly reflected.
- */
- if (vmx->nested.enlightened_vmcs_enabled && !vmx->nested.hv_evmcs)
- nested_vmx_handle_enlightened_vmptrld(vcpu, false);
-
if (vmx->nested.hv_evmcs) {
copy_vmcs12_to_enlightened(vmx);
/* All fields are clean */
@@ -3053,6 +3045,14 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
struct page *page;
u64 hpa;

+ /*
+ * hv_evmcs may end up being not mapped after migration (when
+ * L2 was running), map it here to make sure vmcs12 changes are
+ * properly reflected.
+ */
+ if (vmx->nested.enlightened_vmcs_enabled && !vmx->nested.hv_evmcs)
+ nested_vmx_handle_enlightened_vmptrld(vcpu, false);
+
if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
/*
* Translate L1 physical address to host physical
@@ -5905,10 +5905,12 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
set_current_vmptr(vmx, kvm_state->hdr.vmx.vmcs12_pa);
} else if (kvm_state->flags & KVM_STATE_NESTED_EVMCS) {
/*
- * Sync eVMCS upon entry as we may not have
- * HV_X64_MSR_VP_ASSIST_PAGE set up yet.
+ * nested_vmx_handle_enlightened_vmptrld() cannot be called
+ * directly from here as HV_X64_MSR_VP_ASSIST_PAGE may not be
+ * restored yet. EVMCS will be mapped from
+ * nested_get_vmcs12_pages().
*/
- vmx->nested.need_vmcs12_to_shadow_sync = true;
+ kvm_make_request(KVM_REQ_GET_VMCS12_PAGES, vcpu);
} else {
return -EINVAL;
}
--
2.24.1
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