[PATCH roundup 2/4] ARM: KVM: avoid "HYP init code too big" error

[Ard Biesheuvel]

(resend with complete cc)

On 9 March 2015 at 20:09, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Fri, Mar 06, 2015 at 03:34:40PM +0100, Ard Biesheuvel wrote:
>> From: Arnd Bergmann <arnd at arndb.de>
>>
>> When building large kernels, the linker will emit lots of veneers
>> into the .hyp.idmap.text section, which causes it to grow beyond
>> one page, and that triggers the build error.
>>
>> This moves the section into .rodata instead, which avoids the
>> veneers and is safe because the code is not executed directly
>> but remapped by the hypervisor into its own executable address
>> space.
>>
>> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
>> [ardb: move the ALIGN() to .rodata as well, update log s/copied/remapped/]
>> Tested-by: Marc Zyngier <marc.zyngier at arm.com>
>> Reviewed-by: Marc Zyngier <marc.zyngier at arm.com>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>  arch/arm/kernel/vmlinux.lds.S | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
>> index b31aa73e8076..2787eb8d3616 100644
>> --- a/arch/arm/kernel/vmlinux.lds.S
>> +++ b/arch/arm/kernel/vmlinux.lds.S
>> @@ -22,11 +22,15 @@
>>       ALIGN_FUNCTION();                                               \
>>       VMLINUX_SYMBOL(__idmap_text_start) = .;                         \
>>       *(.idmap.text)                                                  \
>> -     VMLINUX_SYMBOL(__idmap_text_end) = .;                           \
>> +     VMLINUX_SYMBOL(__idmap_text_end) = .;
>> +
>> +#define IDMAP_RODATA                                                 \
>> +     .rodata : {                                                     \
>
> We already have a .rodata section defined by RO_DATA().  Quite how this
> interacts with the existing .rodata section, I don't know, but it
> probably won't be right.  Have you checked what effect this has?
>

 Here's just the rodata lines from 'readelf -S vmlinux', with and
without the patch applied

[ 4] .rodata           PROGBITS        c0752000 552000 310620 00   A  0   0 64

[ 4] .rodata           PROGBITS        c0752000 552000 3106c0 00  AX  0   0 64

and there is only a single one, so it appears binutils is quite happy with this.

If the A -> AX bothers you, we could fold in the following hunk as well.

--- a/arch/arm/kvm/init.S
+++ b/arch/arm/kvm/init.S
@@ -52,7 +52,7 @@
  */

        .text
-       .pushsection    .hyp.idmap.text,"ax"
+       .pushsection    .hyp.idmap.text,"a"
        .align 5
 __kvm_hyp_init:
        .globl __kvm_hyp_init

which takes care of that.