Re: [PATCH] kvm: arm64: correctly align nVHE percpu data

[David Brazdil <dbrazdil@google.com>]

Thanks Jamie

On Fri, Nov 13, 2020 at 03:04:06PM +0000, Jamie Iles wrote:
> The nVHE percpu data is partially linked but the nVHE linker script did
> not align the percpu section.  The PERCPU_INPUT macro would then align
> the data to a page boundary:
> 
>   #define PERCPU_INPUT(cacheline)					\
>   	__per_cpu_start = .;						\
>   	*(.data..percpu..first)						\
>   	. = ALIGN(PAGE_SIZE);						\
>   	*(.data..percpu..page_aligned)					\
>   	. = ALIGN(cacheline);						\
>   	*(.data..percpu..read_mostly)					\
>   	. = ALIGN(cacheline);						\
>   	*(.data..percpu)						\
>   	*(.data..percpu..shared_aligned)				\
>   	PERCPU_DECRYPTED_SECTION					\
>   	__per_cpu_end = .;
> 
> but then when the final vmlinux linking happens the hypervisor percpu
> data is included after page alignment and so the offsets potentially
> don't match.  On my build I saw that the .hyp.data..percpu section was
> at address 0x20 and then the percpu data would begin at 0x1000 (because
> of the page alignment in PERCPU_INPUT), but when linked into vmlinux,
> everything would be shifted down by 0x20 bytes.
> 
> This manifests as one of the CPUs getting lost when running
> kvm-unit-tests or starting any VM and subsequent soft lockup on a Cortex
> A72 device.
> 
> Fixes: 30c953911c43 ("kvm: arm64: Set up hyp percpu data for nVHE")
> Cc: David Brazdil <dbrazdil@google.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Will Deacon <will@kernel.org>

Acked-by: David Brazdil <dbrazdil@google.com>

> Signed-off-by: Jamie Iles <jamie@nuviainc.com>
> ---
> v2: add clarifying commentary
> 
>  arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
> index bb2d986ff696..a797abace13f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
> @@ -13,6 +13,11 @@
>  
>  SECTIONS {
>  	HYP_SECTION(.text)
> +	/*
> +	 * .hyp..data..percpu needs to be page aligned to maintain the same
> +	 * alignment for when linking into vmlinux.
> +	 */
> +	. = ALIGN(PAGE_SIZE);
>  	HYP_SECTION_NAME(.data..percpu) : {
>  		PERCPU_INPUT(L1_CACHE_BYTES)
>  	}
> -- 
> 2.27.0
> 

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