From 5a8781607e677eda60b20e0a4c91d2a5f12f9244 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 25 Jan 2019 07:41:02 -0800 Subject: [PATCH] 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 Reviewed-by: Jim Mattson Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/nested.c | 24 ++++++------------------ arch/x86/kvm/vmx/vmcs.h | 1 + arch/x86/kvm/vmx/vmx.c | 13 ++++++------- arch/x86/kvm/vmx/vmx.h | 1 - 4 files changed, 13 insertions(+), 26 deletions(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 23a2c1b..0e67649 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -1980,17 +1980,6 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12) prepare_vmcs02_early_full(vmx, vmcs12); /* - * 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. host_rsp will - * also be written unconditionally by nested_vmx_check_vmentry_hw() - * if we are doing early consistency checks via hardware. - */ - vmx->host_rsp = 0; - - /* * PIN CONTROLS */ exec_control = vmcs12->pin_based_vm_exec_control; @@ -2754,8 +2743,11 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu) asm( "sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */ + "cmp %%" _ASM_SP ", %c[host_state_rsp](%[loaded_vmcs]) \n\t" + "je 1f \n\t" __ex("vmwrite %%" _ASM_SP ", %[HOST_RSP]") "\n\t" - "mov %%" _ASM_SP ", %c[host_rsp](%% " _ASM_CX ")\n\t" + "mov %%" _ASM_SP ", %c[host_state_rsp](%[loaded_vmcs]) \n\t" + "1: \n\t" "add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */ /* Check if vmlaunch or vmresume is needed */ @@ -2771,11 +2763,10 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu) CC_SET(be) : ASM_CALL_CONSTRAINT, CC_OUT(be) (vm_fail) - : "c"(vmx), - [HOST_RSP]"r"((unsigned long)HOST_RSP), + : [HOST_RSP]"r"((unsigned long)HOST_RSP), [loaded_vmcs]"r"(vmx->loaded_vmcs), [launched]"i"(offsetof(struct loaded_vmcs, launched)), - [host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)), + [host_state_rsp]"i"(offsetof(struct loaded_vmcs, host_state.rsp)), [wordsize]"i"(sizeof(ulong)) : "cc", "memory" ); @@ -3912,9 +3903,6 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason, vmx_flush_tlb(vcpu, true); } - /* This is needed for same reason as it was needed in prepare_vmcs02 */ - vmx->host_rsp = 0; - /* Unpin physical memory we referred to in vmcs02 */ if (vmx->nested.apic_access_page) { kvm_release_page_dirty(vmx->nested.apic_access_page); diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h index 6def3ba..cb6079f 100644 --- a/arch/x86/kvm/vmx/vmcs.h +++ b/arch/x86/kvm/vmx/vmcs.h @@ -34,6 +34,7 @@ struct vmcs_host_state { unsigned long cr4; /* May not match real cr4 */ unsigned long gs_base; unsigned long fs_base; + unsigned long rsp; u16 fs_sel, gs_sel, ldt_sel; #ifdef CONFIG_X86_64 diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index e9d81cd..12bb61e 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6381,9 +6381,9 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx) "sub $%c[wordsize], %%" _ASM_SP "\n\t" /* placeholder for guest RCX */ "push %%" _ASM_CX " \n\t" "sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */ - "cmp %%" _ASM_SP ", %c[host_rsp](%%" _ASM_CX ") \n\t" + "cmp %%" _ASM_SP ", (%%" _ASM_DI ") \n\t" "je 1f \n\t" - "mov %%" _ASM_SP ", %c[host_rsp](%%" _ASM_CX ") \n\t" + "mov %%" _ASM_SP ", (%%" _ASM_DI ") \n\t" /* Avoid VMWRITE when Enlightened VMCS is in use */ "test %%" _ASM_SI ", %%" _ASM_SI " \n\t" "jz 2f \n\t" @@ -6482,11 +6482,10 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx) "xor %%edi, %%edi \n\t" "xor %%ebp, %%ebp \n\t" "pop %%" _ASM_BP " \n\t" - : ASM_CALL_CONSTRAINT, "=S"((int){0}) - : "c"(vmx), "S"(evmcs_rsp), + : ASM_CALL_CONSTRAINT, "=D"((int){0}), "=S"((int){0}) + : "c"(vmx), "D"(&vmx->loaded_vmcs->host_state.rsp), "S"(evmcs_rsp), [launched]"i"(offsetof(struct vcpu_vmx, __launched)), [fail]"i"(offsetof(struct vcpu_vmx, fail)), - [host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)), [HOST_RSP]"i"(HOST_RSP), [rax]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RAX])), [rbx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RBX])), @@ -6509,10 +6508,10 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx) [wordsize]"i"(sizeof(ulong)) : "cc", "memory" #ifdef CONFIG_X86_64 - , "rax", "rbx", "rdx", "rdi" + , "rax", "rbx", "rdx" , "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15" #else - , "eax", "ebx", "edx", "edi" + , "eax", "ebx", "edx" #endif ); } diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index 9932895..8e203b7 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -175,7 +175,6 @@ struct nested_vmx { struct vcpu_vmx { struct kvm_vcpu vcpu; - unsigned long host_rsp; u8 fail; u8 msr_bitmap_mode; u32 exit_intr_info; -- 2.7.4