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KVM: VMX: Optimize VMX instruction error and fault handling
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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
3901336, "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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Sean Christopherson authored and Paolo Bonzini committed Sep 25, 2019
1 parent 4b526de commit 52a9fcb
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Showing 2 changed files with 74 additions and 32 deletions.
72 changes: 40 additions & 32 deletions arch/x86/kvm/vmx/ops.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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)
Expand All @@ -213,23 +227,17 @@ 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)
{
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)
Expand Down
34 changes: 34 additions & 0 deletions arch/x86/kvm/vmx/vmx.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
/*
Expand Down

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