Re: [PATCH 4/5] KVM: nVMX: implement enlightened VMPTRLD and VMCLEAR

Liran Alon
2018-06-14T23:29:18Z

----- vkuznets@redhat.com wrote:

> Per Hyper-V TLFS 5.0b:
>
> "The L1 hypervisor may choose to use enlightened VMCSs by writing 1
> to
> the corresponding field in the VP assist page (see section 7.8.7).
> Another field in the VP assist page controls the currently active
> enlightened VMCS. Each enlightened VMCS is exactly one page (4 KB) in
> size and must be initially zeroed. No VMPTRLD instruction must be
> executed to make an enlightened VMCS active or current.
>
> After the L1 hypervisor performs a VM entry with an enlightened VMCS,
> the VMCS is considered active on the processor. An enlightened VMCS
> can only be active on a single processor at the same time. The L1
> hypervisor can execute a VMCLEAR instruction to transition an
> enlightened VMCS from the active to the non-active state. Any VMREAD
> or VMWRITE instructions while an enlightened VMCS is active is
> unsupported and can result in unexpected behavior."
>
> Keep Enlightened VMCS structure for the current L2 guest permanently
> mapped
> from struct nested_vmx instead of mapping it every time.
>
> Suggested-by: Ladi Prosek <lprosek@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/vmx.c | 98
> ++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 91 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index e7fa9f9c6e36..6802ba91468c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -20,6 +20,7 @@
> #include "mmu.h"
> #include "cpuid.h"
> #include "lapic.h"
> +#include "hyperv.h"
>
> #include <linux/kvm_host.h>
> #include <linux/module.h>
> @@ -690,6 +691,8 @@ struct nested_vmx {
> bool guest_mode;
> } smm;
>
> + gpa_t hv_evmcs_vmptr;
> + struct page *hv_evmcs_page;
> struct hv_enlightened_vmcs *hv_evmcs;
> };
>
> @@ -7695,7 +7698,9 @@ static void nested_vmx_failInvalid(struct
> kvm_vcpu *vcpu)
> static void nested_vmx_failValid(struct kvm_vcpu *vcpu,
> u32 vm_instruction_error)
> {
> - if (to_vmx(vcpu)->nested.current_vmptr == -1ull) {
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> + if (vmx->nested.current_vmptr == -1ull && !vmx->nested.hv_evmcs) {
> /*
> * failValid writes the error number to the current VMCS, which
> * can't be done there isn't a current VMCS.
> @@ -8003,6 +8008,18 @@ static void vmx_disable_shadow_vmcs(struct
> vcpu_vmx *vmx)
> vmcs_write64(VMCS_LINK_POINTER, -1ull);
> }
>
> +static inline void nested_release_evmcs(struct vcpu_vmx *vmx)
> +{
> + if (!vmx->nested.hv_evmcs)
> + return;
> +
> + kunmap(vmx->nested.hv_evmcs_page);
> + kvm_release_page_dirty(vmx->nested.hv_evmcs_page);
> + vmx->nested.hv_evmcs_vmptr = -1ull;
> + vmx->nested.hv_evmcs_page = NULL;
> + vmx->nested.hv_evmcs = NULL;
> +}
> +
> static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
> {
> if (vmx->nested.current_vmptr == -1ull)
> @@ -8062,6 +8079,8 @@ static void free_nested(struct vcpu_vmx *vmx)
> vmx->nested.pi_desc = NULL;
> }
>
> + nested_release_evmcs(vmx);
> +
> free_loaded_vmcs(&vmx->nested.vmcs02);
> }
>
> @@ -8098,12 +8117,18 @@ static int handle_vmclear(struct kvm_vcpu
> *vcpu)
> return kvm_skip_emulated_instruction(vcpu);
> }
>
> - if (vmptr == vmx->nested.current_vmptr)
> - nested_release_vmcs12(vmx);
> + if (vmx->nested.hv_evmcs_page) {
> + if (vmptr == vmx->nested.hv_evmcs_vmptr)
> + nested_release_evmcs(vmx);
> + } else {
> + if (vmptr == vmx->nested.current_vmptr)
> + nested_release_vmcs12(vmx);
>
> - kvm_vcpu_write_guest(vcpu,
> - vmptr + offsetof(struct vmcs12, launch_state),
> - &zero, sizeof(zero));
> + kvm_vcpu_write_guest(vcpu,
> + vmptr + offsetof(struct vmcs12,
> + launch_state),
> + &zero, sizeof(zero));
> + }
>
> nested_vmx_succeed(vcpu);
> return kvm_skip_emulated_instruction(vcpu);
> @@ -8814,6 +8839,10 @@ static int handle_vmptrld(struct kvm_vcpu
> *vcpu)
> return kvm_skip_emulated_instruction(vcpu);
> }
>
> + /* Forbid normal VMPTRLD if Enlightened version was used */
> + if (vmx->nested.hv_evmcs)
> + return 1;
> +
> if (vmx->nested.current_vmptr != vmptr) {
> struct vmcs12 *new_vmcs12;
> struct page *page;
> @@ -8847,6 +8876,55 @@ static int handle_vmptrld(struct kvm_vcpu
> *vcpu)
> return kvm_skip_emulated_instruction(vcpu);
> }
>
> +/*
> + * This is an equivalent of the nested hypervisor executing the
> vmptrld
> + * instruction.
> + */
> +static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu
> *vcpu)
> +{
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> + struct hv_vp_assist_page assist_page;
> +
> + if (likely(!vmx->nested.enlightened_vmcs_enabled))
> + return 1;
> +
> + if (unlikely(!kvm_hv_get_assist_page(vcpu, &assist_page)))
> + return 1;
> +
> + if (unlikely(!assist_page.enlighten_vmentry))
> + return 1;
> +
> + if (unlikely(assist_page.current_nested_vmcs !=
> + vmx->nested.hv_evmcs_vmptr)) {
> +
> + if (!vmx->nested.hv_evmcs)
> + vmx->nested.current_vmptr = -1ull;
> +
> + nested_release_evmcs(vmx);
> +
> + vmx->nested.hv_evmcs_page = kvm_vcpu_gpa_to_page(
> + vcpu, assist_page.current_nested_vmcs);
> +
> + if (unlikely(is_error_page(vmx->nested.hv_evmcs_page)))
> + return 0;
> +
> + vmx->nested.hv_evmcs = kmap(vmx->nested.hv_evmcs_page);
> + vmx->nested.dirty_vmcs12 = true;
> + vmx->nested.hv_evmcs_vmptr = assist_page.current_nested_vmcs;
> +
> + /*
> + * Unlike normal vmcs12, enlightened vmcs12 is not fully
> + * reloaded from guest's memory (read only fields, fields not
> + * present in struct hv_enlightened_vmcs, ...). Make sure there
> + * are no leftovers.
> + */
> + memset(vmx->nested.cached_vmcs12, 0,
> + sizeof(*vmx->nested.cached_vmcs12));
> +
> + }
> + return 1;
> +}
> +
> /* Emulate the VMPTRST instruction */
> static int handle_vmptrst(struct kvm_vcpu *vcpu)
> {
> @@ -8858,6 +8936,9 @@ static int handle_vmptrst(struct kvm_vcpu
> *vcpu)
> if (!nested_vmx_check_permission(vcpu))
> return 1;
>
> + if (unlikely(to_vmx(vcpu)->nested.hv_evmcs))
> + return 1;
> +
> if (get_vmx_mem_address(vcpu, exit_qualification,
> vmx_instruction_info, true, &vmcs_gva))
> return 1;
> @@ -12148,7 +12229,10 @@ static int nested_vmx_run(struct kvm_vcpu
> *vcpu, bool launch)
> if (!nested_vmx_check_permission(vcpu))
> return 1;
>
> - if (!nested_vmx_check_vmcs12(vcpu))
> + if (!nested_vmx_handle_enlightened_vmptrld(vcpu))
> + return 1;
> +
> + if (!vmx->nested.hv_evmcs && !nested_vmx_check_vmcs12(vcpu))
> goto out;
>
> vmcs12 = get_vmcs12(vcpu);
> --
> 2.14.4

Reviewed-By: Liran Alon <liran.alon@oracle.com>