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Subject[PATCH v2 2/5] KVM: VMX: Optimize VMX instruction error and fault handling
Date
Rework the VMX instruction helpers using asm-goto to branch directly
to error/fault "handlers" in lieu of using __ex(), i.e. the generic
____kvm_handle_fault_on_reboot(). Branching directly to fault handling
code during fixup avoids the extra JMP that is inserted after every VMX
instruction when using the generic "fault on reboot" (see commit
3901336ed9887, "x86/kvm: Don't call kvm_spurious_fault() from .fixup").

Opportunistically clean up the helpers so that they all have consistent
error handling and messages.

Leave the usage of ____kvm_handle_fault_on_reboot() (via __ex()) in
kvm_cpu_vmxoff() and nested_vmx_check_vmentry_hw() as is. The VMXOFF
case is not a fast path, i.e. the cleanliness of __ex() is worth the
JMP, and the extra JMP in nested_vmx_check_vmentry_hw() is unavoidable.

Note, VMREAD cannot get the asm-goto treatment as output operands aren't
compatible with GCC's asm-goto due to internal compiler restrictions.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/vmx/ops.h | 72 +++++++++++++++++++++++-------------------
arch/x86/kvm/vmx/vmx.c | 34 ++++++++++++++++++++
2 files changed, 74 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kvm/vmx/ops.h b/arch/x86/kvm/vmx/ops.h
index 2200fb698dd0..79e25d49d4d9 100644
--- a/arch/x86/kvm/vmx/ops.h
+++ b/arch/x86/kvm/vmx/ops.h
@@ -14,6 +14,12 @@
#define __ex_clear(x, reg) \
____kvm_handle_fault_on_reboot(x, "xor " reg ", " reg)

+void vmwrite_error(unsigned long field, unsigned long value);
+void vmclear_error(struct vmcs *vmcs, u64 phys_addr);
+void vmptrld_error(struct vmcs *vmcs, u64 phys_addr);
+void invvpid_error(unsigned long ext, u16 vpid, gva_t gva);
+void invept_error(unsigned long ext, u64 eptp, gpa_t gpa);
+
static __always_inline void vmcs_check16(unsigned long field)
{
BUILD_BUG_ON_MSG(__builtin_constant_p(field) && ((field) & 0x6001) == 0x2000,
@@ -103,21 +109,39 @@ static __always_inline unsigned long vmcs_readl(unsigned long field)
return __vmcs_readl(field);
}

-static noinline void vmwrite_error(unsigned long field, unsigned long value)
-{
- printk(KERN_ERR "vmwrite error: reg %lx value %lx (err %d)\n",
- field, value, vmcs_read32(VM_INSTRUCTION_ERROR));
- dump_stack();
-}
+#define vmx_asm1(insn, op1, error_args...) \
+do { \
+ asm_volatile_goto("1: " __stringify(insn) " %0\n\t" \
+ ".byte 0x2e\n\t" /* branch not taken hint */ \
+ "jna %l[error]\n\t" \
+ _ASM_EXTABLE(1b, %l[fault]) \
+ : : op1 : "cc" : error, fault); \
+ return; \
+error: \
+ insn##_error(error_args); \
+ return; \
+fault: \
+ kvm_spurious_fault(); \
+} while (0)
+
+#define vmx_asm2(insn, op1, op2, error_args...) \
+do { \
+ asm_volatile_goto("1: " __stringify(insn) " %1, %0\n\t" \
+ ".byte 0x2e\n\t" /* branch not taken hint */ \
+ "jna %l[error]\n\t" \
+ _ASM_EXTABLE(1b, %l[fault]) \
+ : : op1, op2 : "cc" : error, fault); \
+ return; \
+error: \
+ insn##_error(error_args); \
+ return; \
+fault: \
+ kvm_spurious_fault(); \
+} while (0)

static __always_inline void __vmcs_writel(unsigned long field, unsigned long value)
{
- bool error;
-
- asm volatile (__ex("vmwrite %2, %1") CC_SET(na)
- : CC_OUT(na) (error) : "r"(field), "rm"(value));
- if (unlikely(error))
- vmwrite_error(field, value);
+ vmx_asm2(vmwrite, "r"(field), "rm"(value), field, value);
}

static __always_inline void vmcs_write16(unsigned long field, u16 value)
@@ -182,28 +206,18 @@ static __always_inline void vmcs_set_bits(unsigned long field, u32 mask)
static inline void vmcs_clear(struct vmcs *vmcs)
{
u64 phys_addr = __pa(vmcs);
- bool error;

- asm volatile (__ex("vmclear %1") CC_SET(na)
- : CC_OUT(na) (error) : "m"(phys_addr));
- if (unlikely(error))
- printk(KERN_ERR "kvm: vmclear fail: %p/%llx\n",
- vmcs, phys_addr);
+ vmx_asm1(vmclear, "m"(phys_addr), vmcs, phys_addr);
}

static inline void vmcs_load(struct vmcs *vmcs)
{
u64 phys_addr = __pa(vmcs);
- bool error;

if (static_branch_unlikely(&enable_evmcs))
return evmcs_load(phys_addr);

- asm volatile (__ex("vmptrld %1") CC_SET(na)
- : CC_OUT(na) (error) : "m"(phys_addr));
- if (unlikely(error))
- printk(KERN_ERR "kvm: vmptrld %p/%llx failed\n",
- vmcs, phys_addr);
+ vmx_asm1(vmptrld, "m"(phys_addr), vmcs, phys_addr);
}

static inline void __invvpid(unsigned long ext, u16 vpid, gva_t gva)
@@ -213,11 +227,8 @@ static inline void __invvpid(unsigned long ext, u16 vpid, gva_t gva)
u64 rsvd : 48;
u64 gva;
} operand = { vpid, 0, gva };
- bool error;

- asm volatile (__ex("invvpid %2, %1") CC_SET(na)
- : CC_OUT(na) (error) : "r"(ext), "m"(operand));
- BUG_ON(error);
+ vmx_asm2(invvpid, "r"(ext), "m"(operand), ext, vpid, gva);
}

static inline void __invept(unsigned long ext, u64 eptp, gpa_t gpa)
@@ -225,11 +236,8 @@ static inline void __invept(unsigned long ext, u64 eptp, gpa_t gpa)
struct {
u64 eptp, gpa;
} operand = {eptp, gpa};
- bool error;

- asm volatile (__ex("invept %2, %1") CC_SET(na)
- : CC_OUT(na) (error) : "r"(ext), "m"(operand));
- BUG_ON(error);
+ vmx_asm2(invept, "r"(ext), "m"(operand), ext, eptp, gpa);
}

static inline bool vpid_sync_vcpu_addr(int vpid, gva_t addr)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 69536553446d..46689019ebf7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -343,6 +343,40 @@ static __always_inline void vmx_disable_intercept_for_msr(unsigned long *msr_bit

void vmx_vmexit(void);

+#define vmx_insn_failed(fmt...) \
+do { \
+ WARN_ONCE(1, fmt); \
+ pr_warn_ratelimited(fmt); \
+} while (0)
+
+noinline void vmwrite_error(unsigned long field, unsigned long value)
+{
+ vmx_insn_failed("kvm: vmwrite failed: field=%lx val=%lx err=%d\n",
+ field, value, vmcs_read32(VM_INSTRUCTION_ERROR));
+}
+
+noinline void vmclear_error(struct vmcs *vmcs, u64 phys_addr)
+{
+ vmx_insn_failed("kvm: vmclear failed: %p/%llx\n", vmcs, phys_addr);
+}
+
+noinline void vmptrld_error(struct vmcs *vmcs, u64 phys_addr)
+{
+ vmx_insn_failed("kvm: vmptrld failed: %p/%llx\n", vmcs, phys_addr);
+}
+
+noinline void invvpid_error(unsigned long ext, u16 vpid, gva_t gva)
+{
+ vmx_insn_failed("kvm: invvpid failed: ext=0x%lx vpid=%u gva=0x%lx\n",
+ ext, vpid, gva);
+}
+
+noinline void invept_error(unsigned long ext, u64 eptp, gpa_t gpa)
+{
+ vmx_insn_failed("kvm: invept failed: ext=0x%lx eptp=%llx gpa=0x%llx\n",
+ ext, eptp, gpa);
+}
+
static DEFINE_PER_CPU(struct vmcs *, vmxarea);
DEFINE_PER_CPU(struct vmcs *, current_vmcs);
/*
--
2.22.0
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