On 09/11/2016 00:00, Junaid Shahid wrote:
> This change adds some symbolic constants for VM Exit Qualifications
> related to EPT Violations and updates handle_ept_violation() to use
> these constants instead of hard-coded numbers.
>
> Signed-off-by: Junaid Shahid <junaids@xxxxxxxxxx>
> ---
> arch/x86/include/asm/vmx.h | 16 ++++++++++++++++
> arch/x86/kvm/vmx.c | 22 ++++++++++++++--------
> 2 files changed, 30 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index a002b07..60991fb 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -465,6 +465,22 @@ struct vmx_msr_entry {
> #define ENTRY_FAIL_VMCS_LINK_PTR 4
>
> /*
> + * Exit Qualifications for EPT Violations
> + */
> +#define EPT_VIOLATION_READ_BIT 0
> +#define EPT_VIOLATION_WRITE_BIT 1
> +#define EPT_VIOLATION_INSTR_BIT 2
> +#define EPT_VIOLATION_READABLE_BIT 3
> +#define EPT_VIOLATION_WRITABLE_BIT 4
> +#define EPT_VIOLATION_EXECUTABLE_BIT 5
> +#define EPT_VIOLATION_READ (1 << EPT_VIOLATION_READ_BIT)
> +#define EPT_VIOLATION_WRITE (1 << EPT_VIOLATION_WRITE_BIT)
> +#define EPT_VIOLATION_INSTR (1 << EPT_VIOLATION_INSTR_BIT)
> +#define EPT_VIOLATION_READABLE (1 << EPT_VIOLATION_READABLE_BIT)
> +#define EPT_VIOLATION_WRITABLE (1 << EPT_VIOLATION_WRITABLE_BIT)
> +#define EPT_VIOLATION_EXECUTABLE (1 << EPT_VIOLATION_EXECUTABLE_BIT)
> +
> +/*
> * VM-instruction error numbers
> */
> enum vm_instruction_error_number {
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index cf1b16d..88e3b02 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6170,14 +6170,20 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
> gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
> trace_kvm_page_fault(gpa, exit_qualification);
>
> - /* it is a read fault? */
> - error_code = (exit_qualification << 2) & PFERR_USER_MASK;
> - /* it is a write fault? */
> - error_code |= exit_qualification & PFERR_WRITE_MASK;
> - /* It is a fetch fault? */
> - error_code |= (exit_qualification << 2) & PFERR_FETCH_MASK;
> - /* ept page table is present? */
> - error_code |= (exit_qualification & 0x38) != 0;
> + /* Is it a read fault? */
> + error_code = ((exit_qualification >> EPT_VIOLATION_READ_BIT) & 1)
> + << PFERR_USER_BIT;
> + /* Is it a write fault? */
> + error_code |= ((exit_qualification >> EPT_VIOLATION_WRITE_BIT) & 1)
> + << PFERR_WRITE_BIT;
> + /* Is it a fetch fault? */
> + error_code |= ((exit_qualification >> EPT_VIOLATION_INSTR_BIT) & 1)
> + << PFERR_FETCH_BIT;
> + /* ept page table entry is present? */
> + error_code |= (((exit_qualification >> EPT_VIOLATION_READABLE_BIT) |
> + (exit_qualification >> EPT_VIOLATION_WRITABLE_BIT) |
> + (exit_qualification >> EPT_VIOLATION_EXECUTABLE_BIT))
> + & 1) << PFERR_PRESENT_BIT;
Please don't change the shape of the condition unnecessarily.
error_code |=
(exit_qualification &
(EPT_VIOLATION_READABLE | EPT_VIOLATION_WRITABLE |
EPT_VIOLATION_EXECUTABLE)) ? PFERR_PRESENT_MASK : 0;
The same form, with the ternary operator, is usable also for the other
cases. GCC generates slightly worse code:
.LFB3:
.cfi_startproc
movl %edi, %eax
shrl $2, %eax
andl $4, %eax
ret
.cfi_endproc
.LFB7:
.cfi_startproc
movl %edi, %eax
movl $4, %edx
andl $16, %eax
cmovne %edx, %eax
ret
but clang gets it right and it can be fixed in the compiler.
Paolo
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