diff options
| author | Sean Christopherson <sean.j.christopherson@intel.com> | 2020-03-26 09:07:12 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-03-31 10:48:11 -0400 |
| commit | 842f4be95899df22b5843ba1a7c8cf37e831a6e8 (patch) | |
| tree | 8691ddc1edcba65b5cb7bbc7a7ad4daf81b4bea5 /arch/x86/kvm/vmx/vmenter.S | |
| parent | 9c14ee21fcf74ac1f31e11180bf0dfd928c912cc (diff) | |
KVM: VMX: Add a trampoline to fix VMREAD error handling
Add a hand coded assembly trampoline to preserve volatile registers
across vmread_error(), and to handle the calling convention differences
between 64-bit and 32-bit due to asmlinkage on vmread_error(). Pass
@field and @fault on the stack when invoking the trampoline to avoid
clobbering volatile registers in the context of the inline assembly.
Calling vmread_error() directly from inline assembly is partially broken
on 64-bit, and completely broken on 32-bit. On 64-bit, it will clobber
%rdi and %rsi (used to pass @field and @fault) and any volatile regs
written by vmread_error(). On 32-bit, asmlinkage means vmread_error()
expects the parameters to be passed on the stack, not via regs.
Opportunistically zero out the result in the trampoline to save a few
bytes of code for every VMREAD. A happy side effect of the trampoline
is that the inline code footprint is reduced by three bytes on 64-bit
due to PUSH/POP being more efficent (in terms of opcode bytes) than MOV.
Fixes: 6e2020977e3e6 ("KVM: VMX: Add error handling to VMREAD helper")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200326160712.28803-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/vmx/vmenter.S')
| -rw-r--r-- | arch/x86/kvm/vmx/vmenter.S | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S index ca2065166d1d..9651ba388ba9 100644 --- a/arch/x86/kvm/vmx/vmenter.S +++ b/arch/x86/kvm/vmx/vmenter.S @@ -234,3 +234,61 @@ SYM_FUNC_START(__vmx_vcpu_run) 2: mov $1, %eax jmp 1b SYM_FUNC_END(__vmx_vcpu_run) + +/** + * vmread_error_trampoline - Trampoline from inline asm to vmread_error() + * @field: VMCS field encoding that failed + * @fault: %true if the VMREAD faulted, %false if it failed + + * Save and restore volatile registers across a call to vmread_error(). Note, + * all parameters are passed on the stack. + */ +SYM_FUNC_START(vmread_error_trampoline) + push %_ASM_BP + mov %_ASM_SP, %_ASM_BP + + push %_ASM_AX + push %_ASM_CX + push %_ASM_DX +#ifdef CONFIG_X86_64 + push %rdi + push %rsi + push %r8 + push %r9 + push %r10 + push %r11 +#endif +#ifdef CONFIG_X86_64 + /* Load @field and @fault to arg1 and arg2 respectively. */ + mov 3*WORD_SIZE(%rbp), %_ASM_ARG2 + mov 2*WORD_SIZE(%rbp), %_ASM_ARG1 +#else + /* Parameters are passed on the stack for 32-bit (see asmlinkage). */ + push 3*WORD_SIZE(%ebp) + push 2*WORD_SIZE(%ebp) +#endif + + call vmread_error + +#ifndef CONFIG_X86_64 + add $8, %esp +#endif + + /* Zero out @fault, which will be popped into the result register. */ + _ASM_MOV $0, 3*WORD_SIZE(%_ASM_BP) + +#ifdef CONFIG_X86_64 + pop %r11 + pop %r10 + pop %r9 + pop %r8 + pop %rsi + pop %rdi +#endif + pop %_ASM_DX + pop %_ASM_CX + pop %_ASM_AX + pop %_ASM_BP + + ret +SYM_FUNC_END(vmread_error_trampoline) |