KVM: nVMX: Prepare vmcs02 from vmcs01 and vmcs12

This patch contains code to prepare the VMCS which can be used to actually
run the L2 guest, vmcs02. prepare_vmcs02 appropriately merges the information
in vmcs12 (the vmcs that L1 built for L2) and in vmcs01 (our desires for our
own guests).
Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/vmx.c

@@ -345,6 +345,12 @@ struct nested_vmx {
 	/* vmcs02_list cache of VMCSs recently used to run L2 guests */
 	struct list_head vmcs02_pool;
 	int vmcs02_num;
+	u64 vmcs01_tsc_offset;
+	/*
+	 * Guest pages referred to in vmcs02 with host-physical pointers, so
+	 * we must keep them pinned while L2 runs.
+	 */
+	struct page *apic_access_page;
 };
 
 struct vcpu_vmx {
@@ -847,6 +853,18 @@ static inline bool report_flexpriority(void)
 	return flexpriority_enabled;
 }
 
+static inline bool nested_cpu_has(struct vmcs12 *vmcs12, u32 bit)
+{
+	return vmcs12->cpu_based_vm_exec_control & bit;
+}
+
+static inline bool nested_cpu_has2(struct vmcs12 *vmcs12, u32 bit)
+{
+	return (vmcs12->cpu_based_vm_exec_control &
+			CPU_BASED_ACTIVATE_SECONDARY_CONTROLS) &&
+		(vmcs12->secondary_vm_exec_control & bit);
+}
+
 static int __find_msr_index(struct vcpu_vmx *vmx, u32 msr)
 {
 	int i;
@@ -1441,6 +1459,22 @@ static void vmx_fpu_activate(struct kvm_vcpu *vcpu)
 
 static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
 
+/*
+ * Return the cr0 value that a nested guest would read. This is a combination
+ * of the real cr0 used to run the guest (guest_cr0), and the bits shadowed by
+ * its hypervisor (cr0_read_shadow).
+ */
+static inline unsigned long nested_read_cr0(struct vmcs12 *fields)
+{
+	return (fields->guest_cr0 & ~fields->cr0_guest_host_mask) |
+		(fields->cr0_read_shadow & fields->cr0_guest_host_mask);
+}
+static inline unsigned long nested_read_cr4(struct vmcs12 *fields)
+{
+	return (fields->guest_cr4 & ~fields->cr4_guest_host_mask) |
+		(fields->cr4_read_shadow & fields->cr4_guest_host_mask);
+}
+
 static void vmx_fpu_deactivate(struct kvm_vcpu *vcpu)
 {
 	vmx_decache_cr0_guest_bits(vcpu);
@@ -3438,6 +3472,9 @@ static void set_cr4_guest_host_mask(struct vcpu_vmx *vmx)
 	vmx->vcpu.arch.cr4_guest_owned_bits = KVM_CR4_GUEST_OWNED_BITS;
 	if (enable_ept)
 		vmx->vcpu.arch.cr4_guest_owned_bits |= X86_CR4_PGE;
+	if (is_guest_mode(&vmx->vcpu))
+		vmx->vcpu.arch.cr4_guest_owned_bits &=
+			~get_vmcs12(&vmx->vcpu)->cr4_guest_host_mask;
 	vmcs_writel(CR4_GUEST_HOST_MASK, ~vmx->vcpu.arch.cr4_guest_owned_bits);
 }
 
@@ -4736,6 +4773,11 @@ static void free_nested(struct vcpu_vmx *vmx)
 		vmx->nested.current_vmptr = -1ull;
 		vmx->nested.current_vmcs12 = NULL;
 	}
+	/* Unpin physical memory we referred to in current vmcs02 */
+	if (vmx->nested.apic_access_page) {
+		nested_release_page(vmx->nested.apic_access_page);
+		vmx->nested.apic_access_page = 0;
+	}
 
 	nested_free_all_saved_vmcss(vmx);
 }
@@ -5810,6 +5852,243 @@ static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
 {
 }
 
+/*
+ * prepare_vmcs02 is called when the L1 guest hypervisor runs its nested
+ * L2 guest. L1 has a vmcs for L2 (vmcs12), and this function "merges" it
+ * with L0's requirements for its guest (a.k.a. vmsc01), so we can run the L2
+ * guest in a way that will both be appropriate to L1's requests, and our
+ * needs. In addition to modifying the active vmcs (which is vmcs02), this
+ * function also has additional necessary side-effects, like setting various
+ * vcpu->arch fields.
+ */
+static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	u32 exec_control;
+
+	vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector);
+	vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector);
+	vmcs_write16(GUEST_SS_SELECTOR, vmcs12->guest_ss_selector);
+	vmcs_write16(GUEST_DS_SELECTOR, vmcs12->guest_ds_selector);
+	vmcs_write16(GUEST_FS_SELECTOR, vmcs12->guest_fs_selector);
+	vmcs_write16(GUEST_GS_SELECTOR, vmcs12->guest_gs_selector);
+	vmcs_write16(GUEST_LDTR_SELECTOR, vmcs12->guest_ldtr_selector);
+	vmcs_write16(GUEST_TR_SELECTOR, vmcs12->guest_tr_selector);
+	vmcs_write32(GUEST_ES_LIMIT, vmcs12->guest_es_limit);
+	vmcs_write32(GUEST_CS_LIMIT, vmcs12->guest_cs_limit);
+	vmcs_write32(GUEST_SS_LIMIT, vmcs12->guest_ss_limit);
+	vmcs_write32(GUEST_DS_LIMIT, vmcs12->guest_ds_limit);
+	vmcs_write32(GUEST_FS_LIMIT, vmcs12->guest_fs_limit);
+	vmcs_write32(GUEST_GS_LIMIT, vmcs12->guest_gs_limit);
+	vmcs_write32(GUEST_LDTR_LIMIT, vmcs12->guest_ldtr_limit);
+	vmcs_write32(GUEST_TR_LIMIT, vmcs12->guest_tr_limit);
+	vmcs_write32(GUEST_GDTR_LIMIT, vmcs12->guest_gdtr_limit);
+	vmcs_write32(GUEST_IDTR_LIMIT, vmcs12->guest_idtr_limit);
+	vmcs_write32(GUEST_ES_AR_BYTES, vmcs12->guest_es_ar_bytes);
+	vmcs_write32(GUEST_CS_AR_BYTES, vmcs12->guest_cs_ar_bytes);
+	vmcs_write32(GUEST_SS_AR_BYTES, vmcs12->guest_ss_ar_bytes);
+	vmcs_write32(GUEST_DS_AR_BYTES, vmcs12->guest_ds_ar_bytes);
+	vmcs_write32(GUEST_FS_AR_BYTES, vmcs12->guest_fs_ar_bytes);
+	vmcs_write32(GUEST_GS_AR_BYTES, vmcs12->guest_gs_ar_bytes);
+	vmcs_write32(GUEST_LDTR_AR_BYTES, vmcs12->guest_ldtr_ar_bytes);
+	vmcs_write32(GUEST_TR_AR_BYTES, vmcs12->guest_tr_ar_bytes);
+	vmcs_writel(GUEST_ES_BASE, vmcs12->guest_es_base);
+	vmcs_writel(GUEST_CS_BASE, vmcs12->guest_cs_base);
+	vmcs_writel(GUEST_SS_BASE, vmcs12->guest_ss_base);
+	vmcs_writel(GUEST_DS_BASE, vmcs12->guest_ds_base);
+	vmcs_writel(GUEST_FS_BASE, vmcs12->guest_fs_base);
+	vmcs_writel(GUEST_GS_BASE, vmcs12->guest_gs_base);
+	vmcs_writel(GUEST_LDTR_BASE, vmcs12->guest_ldtr_base);
+	vmcs_writel(GUEST_TR_BASE, vmcs12->guest_tr_base);
+	vmcs_writel(GUEST_GDTR_BASE, vmcs12->guest_gdtr_base);
+	vmcs_writel(GUEST_IDTR_BASE, vmcs12->guest_idtr_base);
+
+	vmcs_write64(GUEST_IA32_DEBUGCTL, vmcs12->guest_ia32_debugctl);
+	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
+		vmcs12->vm_entry_intr_info_field);
+	vmcs_write32(VM_ENTRY_EXCEPTION_ERROR_CODE,
+		vmcs12->vm_entry_exception_error_code);
+	vmcs_write32(VM_ENTRY_INSTRUCTION_LEN,
+		vmcs12->vm_entry_instruction_len);
+	vmcs_write32(GUEST_INTERRUPTIBILITY_INFO,
+		vmcs12->guest_interruptibility_info);
+	vmcs_write32(GUEST_ACTIVITY_STATE, vmcs12->guest_activity_state);
+	vmcs_write32(GUEST_SYSENTER_CS, vmcs12->guest_sysenter_cs);
+	vmcs_writel(GUEST_DR7, vmcs12->guest_dr7);
+	vmcs_writel(GUEST_RFLAGS, vmcs12->guest_rflags);
+	vmcs_writel(GUEST_PENDING_DBG_EXCEPTIONS,
+		vmcs12->guest_pending_dbg_exceptions);
+	vmcs_writel(GUEST_SYSENTER_ESP, vmcs12->guest_sysenter_esp);
+	vmcs_writel(GUEST_SYSENTER_EIP, vmcs12->guest_sysenter_eip);
+
+	vmcs_write64(VMCS_LINK_POINTER, -1ull);
+
+	vmcs_write32(PIN_BASED_VM_EXEC_CONTROL,
+		(vmcs_config.pin_based_exec_ctrl |
+		 vmcs12->pin_based_vm_exec_control));
+
+	/*
+	 * Whether page-faults are trapped is determined by a combination of
+	 * 3 settings: PFEC_MASK, PFEC_MATCH and EXCEPTION_BITMAP.PF.
+	 * If enable_ept, L0 doesn't care about page faults and we should
+	 * set all of these to L1's desires. However, if !enable_ept, L0 does
+	 * care about (at least some) page faults, and because it is not easy
+	 * (if at all possible?) to merge L0 and L1's desires, we simply ask
+	 * to exit on each and every L2 page fault. This is done by setting
+	 * MASK=MATCH=0 and (see below) EB.PF=1.
+	 * Note that below we don't need special code to set EB.PF beyond the
+	 * "or"ing of the EB of vmcs01 and vmcs12, because when enable_ept,
+	 * vmcs01's EB.PF is 0 so the "or" will take vmcs12's value, and when
+	 * !enable_ept, EB.PF is 1, so the "or" will always be 1.
+	 *
+	 * A problem with this approach (when !enable_ept) is that L1 may be
+	 * injected with more page faults than it asked for. This could have
+	 * caused problems, but in practice existing hypervisors don't care.
+	 * To fix this, we will need to emulate the PFEC checking (on the L1
+	 * page tables), using walk_addr(), when injecting PFs to L1.
+	 */
+	vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK,
+		enable_ept ? vmcs12->page_fault_error_code_mask : 0);
+	vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH,
+		enable_ept ? vmcs12->page_fault_error_code_match : 0);
+
+	if (cpu_has_secondary_exec_ctrls()) {
+		u32 exec_control = vmx_secondary_exec_control(vmx);
+		if (!vmx->rdtscp_enabled)
+			exec_control &= ~SECONDARY_EXEC_RDTSCP;
+		/* Take the following fields only from vmcs12 */
+		exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
+		if (nested_cpu_has(vmcs12,
+				CPU_BASED_ACTIVATE_SECONDARY_CONTROLS))
+			exec_control |= vmcs12->secondary_vm_exec_control;
+
+		if (exec_control & SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES) {
+			/*
+			 * Translate L1 physical address to host physical
+			 * address for vmcs02. Keep the page pinned, so this
+			 * physical address remains valid. We keep a reference
+			 * to it so we can release it later.
+			 */
+			if (vmx->nested.apic_access_page) /* shouldn't happen */
+				nested_release_page(vmx->nested.apic_access_page);
+			vmx->nested.apic_access_page =
+				nested_get_page(vcpu, vmcs12->apic_access_addr);
+			/*
+			 * If translation failed, no matter: This feature asks
+			 * to exit when accessing the given address, and if it
+			 * can never be accessed, this feature won't do
+			 * anything anyway.
+			 */
+			if (!vmx->nested.apic_access_page)
+				exec_control &=
+				  ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
+			else
+				vmcs_write64(APIC_ACCESS_ADDR,
+				  page_to_phys(vmx->nested.apic_access_page));
+		}
+
+		vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
+	}
+
+
+	/*
+	 * Set host-state according to L0's settings (vmcs12 is irrelevant here)
+	 * Some constant fields are set here by vmx_set_constant_host_state().
+	 * Other fields are different per CPU, and will be set later when
+	 * vmx_vcpu_load() is called, and when vmx_save_host_state() is called.
+	 */
+	vmx_set_constant_host_state();
+
+	/*
+	 * HOST_RSP is normally set correctly in vmx_vcpu_run() just before
+	 * entry, but only if the current (host) sp changed from the value
+	 * we wrote last (vmx->host_rsp). This cache is no longer relevant
+	 * if we switch vmcs, and rather than hold a separate cache per vmcs,
+	 * here we just force the write to happen on entry.
+	 */
+	vmx->host_rsp = 0;
+
+	exec_control = vmx_exec_control(vmx); /* L0's desires */
+	exec_control &= ~CPU_BASED_VIRTUAL_INTR_PENDING;
+	exec_control &= ~CPU_BASED_VIRTUAL_NMI_PENDING;
+	exec_control &= ~CPU_BASED_TPR_SHADOW;
+	exec_control |= vmcs12->cpu_based_vm_exec_control;
+	/*
+	 * Merging of IO and MSR bitmaps not currently supported.
+	 * Rather, exit every time.
+	 */
+	exec_control &= ~CPU_BASED_USE_MSR_BITMAPS;
+	exec_control &= ~CPU_BASED_USE_IO_BITMAPS;
+	exec_control |= CPU_BASED_UNCOND_IO_EXITING;
+
+	vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, exec_control);
+
+	/* EXCEPTION_BITMAP and CR0_GUEST_HOST_MASK should basically be the
+	 * bitwise-or of what L1 wants to trap for L2, and what we want to
+	 * trap. Note that CR0.TS also needs updating - we do this later.
+	 */
+	update_exception_bitmap(vcpu);
+	vcpu->arch.cr0_guest_owned_bits &= ~vmcs12->cr0_guest_host_mask;
+	vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
+
+	/* Note: IA32_MODE, LOAD_IA32_EFER are modified by vmx_set_efer below */
+	vmcs_write32(VM_EXIT_CONTROLS,
+		vmcs12->vm_exit_controls | vmcs_config.vmexit_ctrl);
+	vmcs_write32(VM_ENTRY_CONTROLS, vmcs12->vm_entry_controls |
+		(vmcs_config.vmentry_ctrl & ~VM_ENTRY_IA32E_MODE));
+
+	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PAT)
+		vmcs_write64(GUEST_IA32_PAT, vmcs12->guest_ia32_pat);
+	else if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT)
+		vmcs_write64(GUEST_IA32_PAT, vmx->vcpu.arch.pat);
+
+
+	set_cr4_guest_host_mask(vmx);
+
+	vmcs_write64(TSC_OFFSET,
+		vmx->nested.vmcs01_tsc_offset + vmcs12->tsc_offset);
+
+	if (enable_vpid) {
+		/*
+		 * Trivially support vpid by letting L2s share their parent
+		 * L1's vpid. TODO: move to a more elaborate solution, giving
+		 * each L2 its own vpid and exposing the vpid feature to L1.
+		 */
+		vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
+		vmx_flush_tlb(vcpu);
+	}
+
+	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_EFER)
+		vcpu->arch.efer = vmcs12->guest_ia32_efer;
+	if (vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE)
+		vcpu->arch.efer |= (EFER_LMA | EFER_LME);
+	else
+		vcpu->arch.efer &= ~(EFER_LMA | EFER_LME);
+	/* Note: modifies VM_ENTRY/EXIT_CONTROLS and GUEST/HOST_IA32_EFER */
+	vmx_set_efer(vcpu, vcpu->arch.efer);
+
+	/*
+	 * This sets GUEST_CR0 to vmcs12->guest_cr0, with possibly a modified
+	 * TS bit (for lazy fpu) and bits which we consider mandatory enabled.
+	 * The CR0_READ_SHADOW is what L2 should have expected to read given
+	 * the specifications by L1; It's not enough to take
+	 * vmcs12->cr0_read_shadow because on our cr0_guest_host_mask we we
+	 * have more bits than L1 expected.
+	 */
+	vmx_set_cr0(vcpu, vmcs12->guest_cr0);
+	vmcs_writel(CR0_READ_SHADOW, nested_read_cr0(vmcs12));
+
+	vmx_set_cr4(vcpu, vmcs12->guest_cr4);
+	vmcs_writel(CR4_READ_SHADOW, nested_read_cr4(vmcs12));
+
+	/* shadow page tables on either EPT or shadow page tables */
+	kvm_set_cr3(vcpu, vmcs12->guest_cr3);
+	kvm_mmu_reset_context(vcpu);
+
+	kvm_register_write(vcpu, VCPU_REGS_RSP, vmcs12->guest_rsp);
+	kvm_register_write(vcpu, VCPU_REGS_RIP, vmcs12->guest_rip);
+}
+
 static int vmx_check_intercept(struct kvm_vcpu *vcpu,
 			       struct x86_instruction_info *info,
 			       enum x86_intercept_stage stage)