Re: [PATCH v3 4/6] xen/arm: mpu: Create boot-time MPU protection regions

[Julien Grall <julien@xxxxxxx>]

Hi Ayan,

On 21/10/2024 16:07, Ayan Kumar Halder wrote:
> On 18/10/2024 23:13, Julien Grall wrote:
> > Hi Ayan,
> > > +.endm
> > > +
> > > +/*
> > > + * Maps the various sections of Xen (described in xen.lds.S) as 
> > > different MPU
> > > + * regions.
> > > + *
> > > + * Inputs:
> > > + *   lr : Address to return to.
> > > + *
> > > + * Clobbers x0 - x5
> > > + *
> > > + */
> > > +FUNC(enable_boot_cpu_mm)
> > > +
> > > +    /* Check if the number of regions exceeded the count specified 
> > > in MPUIR_EL2 */
> > AFAIU, this doesn't match what the instruction is doing below.
> Sorry, this needs to be removed.
> > > +    mrs   x5, MPUIR_EL2
> > > +
> > > +    /* x0: region sel */
> > > +    mov   x0, xzr
> > > +    /* Xen text section. */
> > > +    load_paddr x1, _stext
> > > +    load_paddr x2, _etext
> > > +    cmp x1, x2
> > > +    beq 1f
> > This check seems to be excessive... I can't think of a reason why 
> > there would be no text at all... Same for a lot of the checks below.
> Is it ok if we have this excess check ? The downsides are only a small 
> increase in code size and boot time. Otherwise, I need to justify why we 
> have this checks in some places, but not in others.
How about moving the check in prepare_xen_region? This should solve the 
concerns on both the current approach and my proposed approach.
Cheers,

--
Julien Grall