On Thu, 26 Mar 2015 22:03:23 +0000
Will Deacon <will.deacon@xxxxxxx> wrote:
> On Thu, Mar 19, 2015 at 01:59:33PM +0000, Marc Zyngier wrote:
> > Since all immediate branches are PC-relative on Aarch64, these
> > instructions cannot be used as an alternative with the simplistic
> > approach we currently have (the immediate has been computed from
> > the .altinstr_replacement section, and end-up being completely off
> > if we insert it directly).
> >
> > This patch handles the b and bl instructions in a different way,
> > using the insn framework to recompute the immediate, and generate
> > the right displacement.
> >
> > Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
> > Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> > ---
> > arch/arm64/kernel/alternative.c | 55 +++++++++++++++++++++++++++++++++++++++--
> > 1 file changed, 53 insertions(+), 2 deletions(-)
>
> [...]
>
> > static int __apply_alternatives(void *alt_region)
> > {
> > struct alt_instr *alt;
> > @@ -40,16 +83,24 @@ static int __apply_alternatives(void *alt_region)
> > u8 *origptr, *replptr;
> >
> > for (alt = region->begin; alt < region->end; alt++) {
> > + u32 insn;
> > + int i;
> > +
> > if (!cpus_have_cap(alt->cpufeature))
> > continue;
> >
> > - BUG_ON(alt->alt_len > alt->orig_len);
> > + BUG_ON(alt->alt_len != alt->orig_len);
> >
> > pr_info_once("patching kernel code\n");
> >
> > origptr = (u8 *)&alt->orig_offset + alt->orig_offset;
> > replptr = (u8 *)&alt->alt_offset + alt->alt_offset;
> > - memcpy(origptr, replptr, alt->alt_len);
> > +
> > + for (i = 0; i < alt->alt_len; i += sizeof(insn)) {
> > + insn = get_alt_insn(origptr + i, replptr + i);
> > + *(u32 *)(origptr + i) = insn;
>
> My brain's not firing on all cylinders right now, but do you need a
> cpu_to_le32 here?
I'm not 100% awake myself (probably some acute form of firmwaritis),
but I suspect you're quite right (get_alt_insn calls aarch64_insn_read,
which does a le32_to_cpu). Obviously, we need to revert the conversion
when writing the instruction back.
Do you want a fixup on top of this, or would you prefer me to respin
the series?
Thanks,
M.
--
Jazz is not dead. It just smells funny.
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