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

[Liran Alon]

----- vkuznets@xxxxxxxxxx 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@xxxxxxxxxx>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>