Re: [PATCH v12 12/12] xen/arm: add cache coloring support for Xen image

[Carlo Nonato <carlo.nonato@xxxxxxxxxxxxxxx>]

Hi Jan,

On Mon, Dec 16, 2024 at 3:36 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 16.12.2024 15:28, Carlo Nonato wrote:
> > On Mon, Dec 16, 2024 at 2:56 PM Michal Orzel <michal.orzel@xxxxxxx> wrote:
> >> On 13/12/2024 17:28, Carlo Nonato wrote:
> >>> --- a/xen/arch/arm/arm64/mmu/mm.c
> >>> +++ b/xen/arch/arm/arm64/mmu/mm.c
> >>> @@ -1,6 +1,7 @@
> >>>  /* SPDX-License-Identifier: GPL-2.0-only */
> >>>
> >>>  #include <xen/init.h>
> >>> +#include <xen/llc-coloring.h>
> >>>  #include <xen/mm.h>
> >>>  #include <xen/pfn.h>
> >>>
> >>> @@ -138,8 +139,36 @@ void update_boot_mapping(bool enable)
> >>>  }
> >>>
> >>>  extern void switch_ttbr_id(uint64_t ttbr);
> >>> +extern void relocate_xen(uint64_t ttbr, void *src, void *dst, size_t 
> >>> len);
> >>>
> >>>  typedef void (switch_ttbr_fn)(uint64_t ttbr);
> >>> +typedef void (relocate_xen_fn)(uint64_t ttbr, void *src, void *dst, 
> >>> size_t len);
> >>> +
> >>> +void __init relocate_and_switch_ttbr(uint64_t ttbr) {
> >> CODING_STYLE: { needs to be on its own line
> >>
> >> Also, this function is only executed in case of LLC coloring, so shouldn't 
> >> it
> >> be #ifdef protected.
> >
> > Here and in other places (patch #8) I'm relying on DCE to remove functions
> > that are not called. This was a suggestion from Jan in that patch. Can we
> > adopt the same here?
>
> Yet how would the compiler spot that the function is unused? That would only
> work with LTO / WPO. DCE (as I did suggest elsewhere) requires the functions
> in question to be static (allowing the compiler to see enough of the whole
> picture).

Sorry, didn't know that. So I will protect with an #ifdef
relocate_and_switch_ttbr() only.

> Jan

Thanks.

- Carlo