Re: [PATCH 5.10] arm64: Do not defer reserve_crashkernel() for platforms with no DMA memory zones

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Apr 04, 2022 at 05:46:10PM -0700, Vijay Balakrishna wrote:
> commit 031495635b4668f94e964e037ca93d0d38bfde58 upstream.
> 
> The following patches resulted in deferring crash kernel reservation to
> mem_init(), mainly aimed at platforms with DMA memory zones (no IOMMU),
> in particular Raspberry Pi 4.
> 
> commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32")
> commit 8424ecdde7df ("arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges")
> commit 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into mem_init()")
> commit 2687275a5843 ("arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required")
> 
> Above changes introduced boot slowdown due to linear map creation for
> all the memory banks with NO_BLOCK_MAPPINGS, see discussion[1].  The proposed
> changes restore crash kernel reservation to earlier behavior thus avoids
> slow boot, particularly for platforms with IOMMU (no DMA memory zones).
> 
> Tested changes to confirm no ~150ms boot slowdown on our SoC with IOMMU
> and 8GB memory.  Also tested with ZONE_DMA and/or ZONE_DMA32 configs to confirm
> no regression to deferring scheme of crash kernel memory reservation.
> In both cases successfully collected kernel crash dump.
> 
> [1] https://lore.kernel.org/all/9436d033-579b-55fa-9b00-6f4b661c2dd7@linux.microsoft.com/
> 
> Signed-off-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
> Cc: stable@vger.kernel.org
> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Link: https://lore.kernel.org/r/1646242689-20744-1-git-send-email-vijayb@linux.microsoft.com
> [will: Add #ifdef CONFIG_KEXEC_CORE guards to fix 'crashk_res' references in allnoconfig build]
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  arch/arm64/mm/init.c | 36 ++++++++++++++++++++++++++++++++----
>  arch/arm64/mm/mmu.c  | 32 +++++++++++++++++++++++++++++++-
>  2 files changed, 63 insertions(+), 5 deletions(-)

Now queued up, thanks.

greg k-h