Re: [PATCH v2 1/2] x86/traps: Initialize DR6 by writing its architectural reset value

[Sohil Mehta <sohil.mehta@intel.com>]

On 6/17/2025 1:47 PM, Sean Christopherson wrote:

> Ah, and now I see that DR6_RESERVED is an existing #define in a uAPI header (Xin
> said there were a few, but I somehow missed them earlier).  Maybe just leave that
> thing alone, but update the comment to state that it's a historical wart?  And
> then put DR6_ACTIVE_LOW and other macros in arch/x86/include/asm/debugreg.h?
> 

Yeah, that's unfortunate. Updating the comment seems the best we do for now.

> /*
>  * DR6_ACTIVE_LOW combines fixed-1 and active-low bits.
>  * We can regard all the bits in DR6_FIXED_1 as active_low bits;
>  * they will never be 0 for now, but when they are defined
>  * in the future it will require no code change.
>  *
>  * DR6_ACTIVE_LOW is also used as the init/reset value for DR6.
>  */
> #define DR6_ACTIVE_LOW	0xffff0ff0
> #define DR6_VOLATILE	0x0001e80f
> #define DR6_FIXED_1	(DR6_ACTIVE_LOW & ~DR6_VOLATILE)