Re: [kvm-unit-tests PATCH 1/2] arm64: set sctlr_el1.SPAN

[Nadav Amit <namit@vmware.com>]

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> On Jul 14, 2023, at 4:29 AM, Shaoqin Huang <shahuang@redhat.com> wrote:
> 
> !! External Email
> 
> Hi,
> 
> On 7/14/23 18:31, Alexandru Elisei wrote:
>> Hi,
>> 
>> On Sat, Jun 17, 2023 at 01:31:37AM +0000, Nadav Amit wrote:
>>> From: Nadav Amit <namit@vmware.com>
>>> 
>>> Do not assume PAN is not supported or that sctlr_el1.SPAN is already set.
>> 
>> In arm/cstart64.S
>> 
>> .globl start
>> start:
>>         /* get our base address */
>>      [..]
>> 
>> 1:
>>         /* zero BSS */
>>      [..]
>> 
>>         /* zero and set up stack */
>>      [..]
>> 
>>         /* set SCTLR_EL1 to a known value */
>>         ldr     x4, =INIT_SCTLR_EL1_MMU_OFF
>>      [..]
>> 
>>         /* set up exception handling */
>>         bl      exceptions_init
>>      [..]
>> 
>> Where in lib/arm64/asm/sysreg.h:
>> 
>> #define SCTLR_EL1_RES1  (_BITUL(7) | _BITUL(8) | _BITUL(11) | _BITUL(20) | \
>>                          _BITUL(22) | _BITUL(23) | _BITUL(28) | _BITUL(29))
>> #define INIT_SCTLR_EL1_MMU_OFF  \
>>                         SCTLR_EL1_RES1
>> 
>> Look like bit 23 (SPAN) should be set.
>> 
>> How are you seeing SCTLR_EL1.SPAN unset?
> 
> Yeah. the sctlr_el1.SPAN has always been set by the above flow. So Nadav
> you can describe what you encounter with more details. Like which tests
> crash you encounter, and how to reproduce it.

I am using Nikos’s work to run the test using EFI, not from QEMU.

So the code that you mentioned - which is supposed to initialize SCTLR -
is not executed (and actually not part of the EFI image).

Note that using EFI, the entry point is _start [1], and not “start”.

That is also the reason lack of BSS zeroing also caused me issues with the
EFI setup, which I reported before.



[1] https://gitlab.com/kvm-unit-tests/kvm-unit-tests/-/blob/master/arm/efi/crt0-efi-aarch64.S#L113


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