From: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
Date: Wed, 25 Jan 2017 12:57:16 -0700
> +static inline void enable_adi(void)
> +{
...
> + __asm__ __volatile__(
> + "rdpr %%pstate, %%g1\n\t"
> + "or %%g1, %0, %%g1\n\t"
> + "wrpr %%g1, %%g0, %%pstate\n\t"
> + ".word 0x83438000\n\t" /* rd %mcdper, %g1 */
> + ".word 0xaf900001\n\t" /* wrpr %g0, %g1, %pmcdper */
> + :
> + : "i" (PSTATE_MCDE)
> + : "g1");
> +}
This is _crazy_ expensive.
This is 4 privileged register operations, every single one incurs a full
pipline flush and virtual cpu thread yield.
And we do this around _every_ single userspace access from the kernel
when the thread has ADI enabled.
I think if the kernel manages the ADI metadata properly, you can get rid
of all of this.
On etrap, you change ESTATE_PSTATE{1,2} to have the MCDE bit enabled.
Then the kernel always runs with ADI enabled.
Furthermore, since the %mcdper register should be set to whatever the
current task has asked for, you should be able to avoid touching it
as well assuming that traps do not change %mcdper's value.
Then you don't need to do anything special during userspace accesses
which seems to be the way this was designed to be used.
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