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KVM: nVMX: stop abusing need_vmcs12_to_shadow_sync for eVMCS mapping 

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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2020-03-09 16:52:12 +01:00 committed by Paolo Bonzini
parent 0c546725ee
commit e942dbf8c5
1 changed files with 13 additions and 11 deletions
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24
arch/x86/kvm/vmx/nested.c
View File

@ -1996,14 +1996,6 @@ 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 */
@ -3062,6 +3054,14 @@ 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
@ -5904,10 +5904,12 @@ 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;
}