Re: [PATCH] ARM64: KVM: Nuke EL2 mode tlbs before enabling MMU for EL2

[Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx>]

Hi Marc,

On 30 July 2014 16:30, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:

Hi Pranav,

On Wed, Jul 30 2014 at 10:46:47 am BST, Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx> wrote:
> X-Gene u-boot runs in EL2 mode with MMU enabled hence we might
> have stale EL2 tlb enteris when we enable EL2 MMU on each host CPU.
>
> This can happen on any ARM64 board running bootloader in EL2
> with MMU enabled.
>
> This patch ensures that we flush all EL2 TLBs on each host CPU
> before enabling EL2 MMU. This is very similar to what we do
> for EL1 TLBs before enabling EL1 MMU.
> (Refer __cpu_setup() of arch/arm64/mm/proc.S)
>
> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx>
> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxx>
> ---
>  arch/arm64/kvm/hyp-init.S |    4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index d968796..c319116 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -80,6 +80,10 @@ __do_hyp_init:
>       msr     mair_el2, x4
>       isb
>
> +     /* Invalidate the stale TLBs from Bootloader */
> +     tlbi    alle2
> +     dsb     sy
> +
>       mrs     x4, sctlr_el2
>       and     x4, x4, #SCTLR_EL2_EE   // preserve endianness of EL2
>       ldr     x5, =SCTLR_EL2_FLAGS

This looks like a valid fix. But I wonder if it wouldn't be better
located in kernel/head.S::el2_setup?

Sure, I can try this on one of my flaky setup where I see this issue :)
One question is , if someone tries to do load/unload KVM module frequently
then do "__do_hyp_init" will require the flushing again ?
 

Also, the 32bit code seems to suffer from the same issue. Care to fix it
as well?

I am fine with this but as I do not have arm32 board to test it somebody will need to add tested-by.

 

Thanks,

        M.
--
Jazz is not dead. It just smells funny.

Thanks,

Pranav

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