lkml.org 
[lkml]   [2021]   [Apr]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC v1 03/26] x86/cpufeatures: Add is_tdx_guest() interface
From
Date


On 4/1/21 2:19 PM, Dave Hansen wrote:
> On 4/1/21 2:15 PM, Kuppuswamy, Sathyanarayanan wrote:
>> On 4/1/21 2:08 PM, Dave Hansen wrote:
>>> On 2/5/21 3:38 PM, Kuppuswamy Sathyanarayanan wrote:
>>>> +bool is_tdx_guest(void)
>>>> +{
>>>> +    return static_cpu_has(X86_FEATURE_TDX_GUEST);
>>>> +}
>>>
>>> Why do you need is_tdx_guest() as opposed to calling
>>> cpu_feature_enabled(X86_FEATURE_TDX_GUEST) everywhere?
>>
>> is_tdx_guest() is also implemented/used in compressed
>> code (which uses native_cpuid calls). I don't think
>> we can use cpu_feature_enabled(X86_FEATURE_TDX_GUEST) in
>> compressed code right? Also is_tdx_guest() looks easy
>> to read and use.
>
> OK, but how many of the is_tdx_guest() uses are in the compressed code?
> Why has its use spread beyond that?
Its only used in handling in/out instructions in compressed code. But this
code shared with in/out handling on non-compressed code.

#define __out(bwl, bw) \
do { \
if (is_tdx_guest()) { \
asm volatile("call tdg_out" #bwl : : \
"a"(value), "d"(port)); \
} else { \
asm volatile("out" #bwl " %" #bw "0, %w1" : : \
"a"(value), "Nd"(port)); \
} \
} while (0)
#define __in(bwl, bw) \
do { \
if (is_tdx_guest()) { \
asm volatile("call tdg_in" #bwl : \
"=a"(value) : "d"(port)); \
} else { \
asm volatile("in" #bwl " %w1, %" #bw "0" : \
"=a"(value) : "Nd"(port)); \
} \
} while (0)

>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

\
 
 \ /
  Last update: 2021-04-02 00:26    [W:0.086 / U:23.368 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site