On Thu, Feb 13, 2025 at 11:03 AM Leo Yan <leo.yan@xxxxxxx> wrote:
>
> On Sun, Feb 02, 2025 at 06:43:04PM -0600, Rob Herring (Arm) wrote:
>
> [...]
>
> > +static void __debug_save_brbe(u64 *brbcr_el1)
> > +{
> > + *brbcr_el1 = 0;
> > +
> > + /* Check if the BRBE is enabled */
> > + if (!(read_sysreg_el1(SYS_BRBCR) & (BRBCR_ELx_E0BRE | BRBCR_ELx_ExBRE)))
> > + return;
> > +
> > + /*
> > + * Prohibit branch record generation while we are in guest.
> > + * Since access to BRBCR_EL1 is trapped, the guest can't
> > + * modify the filtering set by the host.
> > + */
> > + *brbcr_el1 = read_sysreg_el1(SYS_BRBCR);
> > + write_sysreg_el1(0, SYS_BRBCR);
> > +}
>
> Should flush branch record and use isb() before exit host kernel?
I don't think so. The isb()'s in the other cases appear to be related
to ordering WRT memory buffers. BRBE is just registers. I would assume
that there's some barrier before we switch to the guest.
> I see inconsistence between the function above and BRBE's disable
> function. Here it clears E0BRE / ExBRE bits for disabling BRBE, but the
> BRBE driver sets the PAUSED bit in BRBFCR_EL1 for disabling BRBE.
Indeed. This works, but the enabled check won't work. I'm going to add
clearing BRBCR to brbe_disable(), and this part will stay the same.
Rob
