Re: [RFC 01/14] x86/apic: Add new driver for Secure AVIC

[Neeraj Upadhyay]

On 11/19/2024 3:15 AM, Melody (Huibo) Wang wrote:
> Hi Neeraj,
> 
> On 9/13/2024 4:36 AM, Neeraj Upadhyay wrote:
>> From: Kishon Vijay Abraham I <kvijayab@xxxxxxx>
>>
>> The Secure AVIC feature provides SEV-SNP guests hardware acceleration
>> for performance sensitive APIC accesses while securely managing the
>> guest-owned APIC state through the use of a private APIC backing page.
>> This helps prevent malicious hypervisor from generating unexpected
>> interrupts for a vCPU or otherwise violate architectural assumptions
>> around APIC behavior.
>>
>> Add a new x2APIC driver that will serve as the base of the Secure AVIC
>> support. It is initially the same as the x2APIC phys driver, but will be
>> modified as features of Secure AVIC are implemented.
>>
>> Signed-off-by: Kishon Vijay Abraham I <kvijayab@xxxxxxx>
>> Co-developed-by: Neeraj Upadhyay <Neeraj.Upadhyay@xxxxxxx>
>> Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@xxxxxxx>
>> ---
>>  arch/x86/Kconfig                    |  12 +++
>>  arch/x86/boot/compressed/sev.c      |   1 +
>>  arch/x86/coco/core.c                |   3 +
>>  arch/x86/include/asm/msr-index.h    |   4 +-
>>  arch/x86/kernel/apic/Makefile       |   1 +
>>  arch/x86/kernel/apic/x2apic_savic.c | 112 ++++++++++++++++++++++++++++
>>  include/linux/cc_platform.h         |   8 ++
>>  7 files changed, 140 insertions(+), 1 deletion(-)
>>  create mode 100644 arch/x86/kernel/apic/x2apic_savic.c
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 007bab9f2a0e..b05b4e9d2e49 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -469,6 +469,18 @@ config X86_X2APIC
>>  
>>  	  If you don't know what to do here, say N.
>>  
>> +config AMD_SECURE_AVIC
>> +	bool "AMD Secure AVIC"
>> +	depends on X86_X2APIC && AMD_MEM_ENCRYPT
> 
> If we remove the dependency on X2APIC, there are only 3 X2APIC functions which you call from this driver. Can we just expose them in the header, and then simply remove the dependency on X2APIC? 
> 

APIC common code (arch/x86/kernel/apic/apic.c) and other parts of the
x86 code use X86_X2APIC config to enable x2apic related initialization
and functionality. So, dependency on X2APIC need to be there.


- Neeraj

> Thanks
> Melody
>