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Subject[PATCH v2 3/5] KVM: VMX: Add error handling to VMREAD helper
Date
Now that VMREAD flows require a taken branch, courtesy of commit

3901336ed9887 ("x86/kvm: Don't call kvm_spurious_fault() from .fixup")

bite the bullet and add full error handling to VMREAD, i.e. replace the
JMP added by __ex()/____kvm_handle_fault_on_reboot() with a hinted Jcc.

To minimize the code footprint, add a helper function, vmread_error(),
to handle both faults and failures so that the inline flow has a single
CALL.

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 | 21 +++++++++++++++++----
arch/x86/kvm/vmx/vmx.c | 8 ++++++++
2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/ops.h b/arch/x86/kvm/vmx/ops.h
index 79e25d49d4d9..45eaedee2ac0 100644
--- a/arch/x86/kvm/vmx/ops.h
+++ b/arch/x86/kvm/vmx/ops.h
@@ -11,9 +11,8 @@
#include "vmcs.h"

#define __ex(x) __kvm_handle_fault_on_reboot(x)
-#define __ex_clear(x, reg) \
- ____kvm_handle_fault_on_reboot(x, "xor " reg ", " reg)

+asmlinkage void vmread_error(unsigned long field, bool fault);
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);
@@ -68,8 +67,22 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
{
unsigned long value;

- asm volatile (__ex_clear("vmread %1, %0", "%k0")
- : "=r"(value) : "r"(field));
+ asm volatile("1: vmread %2, %1\n\t"
+ ".byte 0x3e\n\t" /* branch taken hint */
+ "ja 3f\n\t"
+ "mov %2, %%" _ASM_ARG1 "\n\t"
+ "xor %%" _ASM_ARG2 ", %%" _ASM_ARG2 "\n\t"
+ "2: call vmread_error\n\t"
+ "xor %k1, %k1\n\t"
+ "3:\n\t"
+
+ ".pushsection .fixup, \"ax\"\n\t"
+ "4: mov %2, %%" _ASM_ARG1 "\n\t"
+ "mov $1, %%" _ASM_ARG2 "\n\t"
+ "jmp 2b\n\t"
+ ".popsection\n\t"
+ _ASM_EXTABLE(1b, 4b)
+ : ASM_CALL_CONSTRAINT, "=r"(value) : "r"(field) : "cc");
return value;
}

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 46689019ebf7..9acf3d6395d3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -349,6 +349,14 @@ do { \
pr_warn_ratelimited(fmt); \
} while (0)

+asmlinkage void vmread_error(unsigned long field, bool fault)
+{
+ if (fault)
+ kvm_spurious_fault();
+ else
+ vmx_insn_failed("kvm: vmread failed: field=%lx\n", field);
+}
+
noinline void vmwrite_error(unsigned long field, unsigned long value)
{
vmx_insn_failed("kvm: vmwrite failed: field=%lx val=%lx err=%d\n",
--
2.22.0
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