Re: [kvm-unit-tests PATCH] x86: vmx: Mask undefined bits in exit qualifications

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

On 06/17/2019 12:52 PM, Nadav Amit wrote:
>> On May 3, 2019, at 10:49 AM, nadav.amit@gmail.com wrote:
>>
>> From: Nadav Amit <nadav.amit@gmail.com>
>>
>> On EPT violation, the exit qualifications may have some undefined bits.
>>
>> Bit 6 is undefined if "mode-based execute control" is 0.
>>
>> Bits 9-11 are undefined unless the processor supports advanced VM-exit
>> information for EPT violations.
>>
>> Right now on KVM these bits are always undefined inside the VM (i.e., in
>> an emulated VM-exit). Mask these bits to avoid potential false
>> indication of failures.
>>
>> Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
>> ---
>> x86/vmx.h       | 20 ++++++++++++--------
>> x86/vmx_tests.c |  4 ++++
>> 2 files changed, 16 insertions(+), 8 deletions(-)
>>
>> diff --git a/x86/vmx.h b/x86/vmx.h
>> index cc377ef..5053d6f 100644
>> --- a/x86/vmx.h
>> +++ b/x86/vmx.h
>> @@ -603,16 +603,20 @@ enum vm_instruction_error_number {
>> #define EPT_ADDR_MASK		GENMASK_ULL(51, 12)
>> #define PAGE_MASK_2M		(~(PAGE_SIZE_2M-1))
>>
>> -#define EPT_VLT_RD		1
>> -#define EPT_VLT_WR		(1 << 1)
>> -#define EPT_VLT_FETCH		(1 << 2)
>> -#define EPT_VLT_PERM_RD		(1 << 3)
>> -#define EPT_VLT_PERM_WR		(1 << 4)
>> -#define EPT_VLT_PERM_EX		(1 << 5)
>> +#define EPT_VLT_RD		(1ull << 0)
>> +#define EPT_VLT_WR		(1ull << 1)
>> +#define EPT_VLT_FETCH		(1ull << 2)
>> +#define EPT_VLT_PERM_RD		(1ull << 3)
>> +#define EPT_VLT_PERM_WR		(1ull << 4)
>> +#define EPT_VLT_PERM_EX		(1ull << 5)
>> +#define EPT_VLT_PERM_USER_EX	(1ull << 6)
>> #define EPT_VLT_PERMS		(EPT_VLT_PERM_RD | EPT_VLT_PERM_WR | \
>> 				 EPT_VLT_PERM_EX)
>> -#define EPT_VLT_LADDR_VLD	(1 << 7)
>> -#define EPT_VLT_PADDR		(1 << 8)
>> +#define EPT_VLT_LADDR_VLD	(1ull << 7)
>> +#define EPT_VLT_PADDR		(1ull << 8)
>> +#define EPT_VLT_GUEST_USER	(1ull << 9)
>> +#define EPT_VLT_GUEST_WR	(1ull << 10)

This one should be named EPT_VLT_GUEST_RW,  assuming you are naming them 
according to the 1-setting of the bits.

>> +#define EPT_VLT_GUEST_EX	(1ull << 11)
>>
>> #define MAGIC_VAL_1		0x12345678ul
>> #define MAGIC_VAL_2		0x87654321ul
>> diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
>> index c52ebc6..b4129e1 100644
>> --- a/x86/vmx_tests.c
>> +++ b/x86/vmx_tests.c
>> @@ -2365,6 +2365,10 @@ static void do_ept_violation(bool leaf, enum ept_access_op op,
>>
>> 	qual = vmcs_read(EXI_QUALIFICATION);
>>
>> +	/* Mask undefined bits (which may later be defined in certain cases). */
>> +	qual &= ~(EPT_VLT_GUEST_USER | EPT_VLT_GUEST_WR | EPT_VLT_GUEST_EX |
>> +		 EPT_VLT_PERM_USER_EX);
>> +

The "DIAGNOSE" macro doesn't check any of these bits, so this masking 
seems redundant.

Also, don't we need to check for the relevant conditions before masking 
the bits ? For example, EPT_VLT_PERM_USER_EX is dependent on "mode-based 
execute control" VM-execution control"  and the other ones depend on bit 
7 and 8 of the Exit Qualification field.

>> 	diagnose_ept_violation_qual(expected_qual, qual);
>> 	TEST_EXPECT_EQ(expected_qual, qual);
>>
>> -- 
>> 2.17.1
> Ping.
>