KVM: nVMX: Cache host_rsp on a per-VMCS basis
Currently, host_rsp is cached on a per-vCPU basis, i.e. it's stored in struct vcpu_vmx. In non-nested usage the caching is for all intents and purposes 100% effective, e.g. only the first VMLAUNCH needs to synchronize VMCS.HOST_RSP since the call stack to vmx_vcpu_run() is identical each and every time. But when running a nested guest, KVM must invalidate the cache when switching the current VMCS as it can't guarantee the new VMCS has the same HOST_RSP as the previous VMCS. In other words, the cache loses almost all of its efficacy when running a nested VM. Move host_rsp to struct vmcs_host_state, which is per-VMCS, so that it is cached on a per-VMCS basis and restores its 100% hit rate when nested VMs are in play. Note that the host_rsp cache for vmcs02 essentially "breaks" when nested early checks are enabled as nested_vmx_check_vmentry_hw() will see a different RSP at the time of its VM-Enter. While it's possible to avoid even that VMCS.HOST_RSP synchronization, e.g. by employing a dedicated VM-Exit stack, there is little motivation for doing so as the overhead of two VMWRITEs (~55 cycles) is dwarfed by the overhead of the extra VMX transition (600+ cycles) and is a proverbial drop in the ocean relative to the total cost of a nested transtion (10s of thousands of cycles). Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Reviewed-by: Jim Mattson <jmattson@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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@ -1979,17 +1979,6 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
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if (vmx->nested.dirty_vmcs12 || vmx->nested.hv_evmcs)
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if (vmx->nested.dirty_vmcs12 || vmx->nested.hv_evmcs)
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prepare_vmcs02_early_full(vmx, vmcs12);
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prepare_vmcs02_early_full(vmx, vmcs12);
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/*
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* HOST_RSP is normally set correctly in vmx_vcpu_run() just before
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* entry, but only if the current (host) sp changed from the value
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* we wrote last (vmx->host_rsp). This cache is no longer relevant
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* if we switch vmcs, and rather than hold a separate cache per vmcs,
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* here we just force the write to happen on entry. host_rsp will
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* also be written unconditionally by nested_vmx_check_vmentry_hw()
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* if we are doing early consistency checks via hardware.
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*/
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vmx->host_rsp = 0;
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/*
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/*
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* PIN CONTROLS
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* PIN CONTROLS
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*/
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*/
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@ -2754,8 +2743,11 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
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asm(
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asm(
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"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */
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"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */
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"cmp %%" _ASM_SP ", %c[host_state_rsp](%[loaded_vmcs]) \n\t"
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"je 1f \n\t"
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__ex("vmwrite %%" _ASM_SP ", %[HOST_RSP]") "\n\t"
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__ex("vmwrite %%" _ASM_SP ", %[HOST_RSP]") "\n\t"
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"mov %%" _ASM_SP ", %c[host_rsp](%% " _ASM_CX ")\n\t"
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"mov %%" _ASM_SP ", %c[host_state_rsp](%[loaded_vmcs]) \n\t"
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"1: \n\t"
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"add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */
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"add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */
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/* Check if vmlaunch or vmresume is needed */
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/* Check if vmlaunch or vmresume is needed */
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@ -2771,11 +2763,10 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
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CC_SET(be)
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CC_SET(be)
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: ASM_CALL_CONSTRAINT, CC_OUT(be) (vm_fail)
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: ASM_CALL_CONSTRAINT, CC_OUT(be) (vm_fail)
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: "c"(vmx),
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: [HOST_RSP]"r"((unsigned long)HOST_RSP),
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[HOST_RSP]"r"((unsigned long)HOST_RSP),
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[loaded_vmcs]"r"(vmx->loaded_vmcs),
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[loaded_vmcs]"r"(vmx->loaded_vmcs),
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[launched]"i"(offsetof(struct loaded_vmcs, launched)),
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[launched]"i"(offsetof(struct loaded_vmcs, launched)),
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[host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)),
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[host_state_rsp]"i"(offsetof(struct loaded_vmcs, host_state.rsp)),
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[wordsize]"i"(sizeof(ulong))
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[wordsize]"i"(sizeof(ulong))
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: "cc", "memory"
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: "cc", "memory"
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);
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);
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@ -3912,9 +3903,6 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
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vmx_flush_tlb(vcpu, true);
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vmx_flush_tlb(vcpu, true);
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}
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}
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/* This is needed for same reason as it was needed in prepare_vmcs02 */
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vmx->host_rsp = 0;
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/* Unpin physical memory we referred to in vmcs02 */
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/* Unpin physical memory we referred to in vmcs02 */
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if (vmx->nested.apic_access_page) {
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if (vmx->nested.apic_access_page) {
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kvm_release_page_dirty(vmx->nested.apic_access_page);
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kvm_release_page_dirty(vmx->nested.apic_access_page);
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@ -34,6 +34,7 @@ struct vmcs_host_state {
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unsigned long cr4; /* May not match real cr4 */
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unsigned long cr4; /* May not match real cr4 */
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unsigned long gs_base;
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unsigned long gs_base;
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unsigned long fs_base;
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unsigned long fs_base;
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unsigned long rsp;
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u16 fs_sel, gs_sel, ldt_sel;
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u16 fs_sel, gs_sel, ldt_sel;
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#ifdef CONFIG_X86_64
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#ifdef CONFIG_X86_64
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@ -6381,9 +6381,9 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
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"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* placeholder for guest RCX */
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"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* placeholder for guest RCX */
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"push %%" _ASM_CX " \n\t"
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"push %%" _ASM_CX " \n\t"
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"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */
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"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */
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"cmp %%" _ASM_SP ", %c[host_rsp](%%" _ASM_CX ") \n\t"
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"cmp %%" _ASM_SP ", (%%" _ASM_DI ") \n\t"
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"je 1f \n\t"
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"je 1f \n\t"
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"mov %%" _ASM_SP ", %c[host_rsp](%%" _ASM_CX ") \n\t"
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"mov %%" _ASM_SP ", (%%" _ASM_DI ") \n\t"
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/* Avoid VMWRITE when Enlightened VMCS is in use */
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/* Avoid VMWRITE when Enlightened VMCS is in use */
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"test %%" _ASM_SI ", %%" _ASM_SI " \n\t"
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"test %%" _ASM_SI ", %%" _ASM_SI " \n\t"
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"jz 2f \n\t"
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"jz 2f \n\t"
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@ -6482,11 +6482,10 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
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"xor %%edi, %%edi \n\t"
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"xor %%edi, %%edi \n\t"
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"xor %%ebp, %%ebp \n\t"
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"xor %%ebp, %%ebp \n\t"
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"pop %%" _ASM_BP " \n\t"
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"pop %%" _ASM_BP " \n\t"
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: ASM_CALL_CONSTRAINT, "=S"((int){0})
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: ASM_CALL_CONSTRAINT, "=D"((int){0}), "=S"((int){0})
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: "c"(vmx), "S"(evmcs_rsp),
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: "c"(vmx), "D"(&vmx->loaded_vmcs->host_state.rsp), "S"(evmcs_rsp),
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[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
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[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
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[fail]"i"(offsetof(struct vcpu_vmx, fail)),
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[fail]"i"(offsetof(struct vcpu_vmx, fail)),
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[host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)),
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[HOST_RSP]"i"(HOST_RSP),
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[HOST_RSP]"i"(HOST_RSP),
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[rax]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RAX])),
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[rax]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RAX])),
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[rbx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RBX])),
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[rbx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RBX])),
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@ -6509,10 +6508,10 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
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[wordsize]"i"(sizeof(ulong))
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[wordsize]"i"(sizeof(ulong))
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: "cc", "memory"
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: "cc", "memory"
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#ifdef CONFIG_X86_64
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#ifdef CONFIG_X86_64
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, "rax", "rbx", "rdx", "rdi"
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, "rax", "rbx", "rdx"
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, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
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, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
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#else
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#else
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, "eax", "ebx", "edx", "edi"
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, "eax", "ebx", "edx"
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#endif
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#endif
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);
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);
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}
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}
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@ -175,7 +175,6 @@ struct nested_vmx {
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struct vcpu_vmx {
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struct vcpu_vmx {
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struct kvm_vcpu vcpu;
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struct kvm_vcpu vcpu;
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unsigned long host_rsp;
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u8 fail;
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u8 fail;
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u8 msr_bitmap_mode;
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u8 msr_bitmap_mode;
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u32 exit_intr_info;
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u32 exit_intr_info;
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