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authorSean Christopherson <sean.j.christopherson@intel.com>2019-01-25 07:41:02 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2019-02-12 13:12:22 +0100
commit5a8781607e677eda60b20e0a4c91d2a5f12f9244 (patch)
tree3ad19b2b68799e509703628520ae4b20f498df7f
parentfbda0fd31a6d683637f848ba17956048dd0c7e48 (diff)
downloadlinux-stericsson-5a8781607e677eda60b20e0a4c91d2a5f12f9244.tar.gz
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>
-rw-r--r--arch/x86/kvm/vmx/nested.c24
-rw-r--r--arch/x86/kvm/vmx/vmcs.h1
-rw-r--r--arch/x86/kvm/vmx/vmx.c13
-rw-r--r--arch/x86/kvm/vmx/vmx.h1
4 files changed, 13 insertions, 26 deletions
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 23a2c1b91389..0e67649e39ce 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 6def3ba88e3b..cb6079f8a227 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 e9d81cd8421f..12bb61e7aca6 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 99328954c2fc..8e203b725928 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;