Re: [Xen-devel] [PATCH v2 30/35] xen/arm32: head: Don't setup the fixmap on secondary CPUs

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 22 Jul 2019, Julien Grall wrote:
> setup_fixmap() will setup the fixmap in the boot page tables in order to
> use earlyprintk and also update the register r11 holding the address to
> the UART.
> 
> However, secondary CPUs are not using earlyprintk between turning the
> MMU on and switching to the runtime page table. So setting up the
> fixmap in the boot pages table is pointless.
> 
> This means most of setup_fixmap() is not necessary for the secondary
> CPUs. The update of UART address is now moved out of setup_fixmap() and
> duplicated in the CPU boot and secondary CPUs boot. Additionally, the
> call to setup_fixmap() is removed from secondary CPUs boot.
> 
> Lastly, take the opportunity to replace load from literal pool with the
> new macro mov_w.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>     Changes in v2:
>         - Patch added
> ---
>  xen/arch/arm/arm32/head.S | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 6dc6032498..0a5c3a8525 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -159,6 +159,10 @@ past_zImage:
>          mov   pc, r0
>  primary_switched:
>          bl    setup_fixmap
> +#ifdef CONFIG_EARLY_PRINTK
> +        /* Use a virtual address to access the UART. */
> +        mov_w r11, EARLY_UART_VIRTUAL_ADDRESS
> +#endif
>          b     launch
>  ENDPROC(start)
>  
> @@ -200,8 +204,6 @@ GLOBAL(init_secondary)
>          ldr   r0, =secondary_switched
>          mov   pc, r0
>  secondary_switched:
> -        bl    setup_fixmap
> -
>          /*
>           * Non-boot CPUs need to move on to the proper pagetables, which were
>           * setup in init_secondary_pagetables.
> @@ -221,6 +223,10 @@ secondary_switched:
>          dsb                          /* Ensure completion of TLB+BP flush */
>          isb
>  
> +#ifdef CONFIG_EARLY_PRINTK
> +        /* Use a virtual address to access the UART. */
> +        mov_w r11, EARLY_UART_VIRTUAL_ADDRESS
> +#endif
>          b     launch
>  ENDPROC(init_secondary)
>  
> @@ -475,13 +481,6 @@ setup_fixmap:
>           */
>          dsb
>  #if defined(CONFIG_EARLY_PRINTK) /* Fixmap is only used by early printk */
> -        /*
> -         * Non-boot CPUs don't need to rebuild the fixmap itself, just
> -         * the mapping from boot_second to xen_fixmap
> -         */
> -        teq   r12, #0
> -        bne   1f
> -
>          /* Add UART to the fixmap table */
>          ldr   r1, =xen_fixmap        /* r1 := vaddr (xen_fixmap) */
>          lsr   r2, r11, #THIRD_SHIFT
> @@ -502,9 +501,6 @@ setup_fixmap:
>          mov   r4, r4, lsr #(SECOND_SHIFT - 3)   /* r4 := Slot for FIXMAP(0) 
> */
>          mov   r3, #0x0
>          strd  r2, r3, [r1, r4]       /* Map it in the fixmap's slot */
> -
> -        /* Use a virtual address to access the UART. */
> -        ldr   r11, =EARLY_UART_VIRTUAL_ADDRESS
>  #endif
>  
>          /*
> -- 
> 2.11.0
> 

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