On Fri, Jul 03, 2020 at 11:58:15AM +0800, Chen Zhou wrote:
> commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32")
> broken the arm64 kdump. If the memory reserved for crash dump kernel
> falled in ZONE_DMA32, the devices in crash dump kernel need to use
> ZONE_DMA will alloc fail.
>
> This patch addressed the above issue based on "reserving crashkernel
> above 4G". Originally, we reserve low memory below 4G, and now just need
> to adjust memory limit to arm64_dma_phys_limit in reserve_crashkernel_low
> if ZONE_DMA is enabled. That is, if there are devices need to use ZONE_DMA
> in crash dump kernel, it is a good choice to use parameters
> "crashkernel=X crashkernel=Y,low".
>
> Signed-off-by: Chen Zhou <chenzhou10@xxxxxxxxxx>
> ---
> kernel/crash_core.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index a7580d291c37..e8ecbbc761a3 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -320,6 +320,7 @@ int __init reserve_crashkernel_low(void)
> unsigned long long base, low_base = 0, low_size = 0;
> unsigned long total_low_mem;
> int ret;
> + phys_addr_t crash_max = 1ULL << 32;
>
> total_low_mem = memblock_mem_size(1UL << (32 - PAGE_SHIFT));
>
> @@ -352,7 +353,11 @@ int __init reserve_crashkernel_low(void)
> return 0;
> }
>
> - low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN);
> +#ifdef CONFIG_ARM64
> + if (IS_ENABLED(CONFIG_ZONE_DMA))
> + crash_max = arm64_dma_phys_limit;
> +#endif
> + low_base = memblock_find_in_range(0, crash_max, low_size, CRASH_ALIGN);
> if (!low_base) {
> pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
> (unsigned long)(low_size >> 20));
Given the number of #ifdefs we end up with in this function, I think
it's better to simply copy to the code to arch/arm64 and tailor it
accordingly.
Anyway, there are two series solving slightly different issues with
kdump reservations:
1. This series which relaxes the crashkernel= allocation to go anywhere
in the accessible space while having a dedicated crashkernel=X,low
option for ZONE_DMA.
2. Bhupesh's series [1] forcing crashkernel=X allocations only from
ZONE_DMA.
For RPi4 support, we limited ZONE_DMA allocations to the 1st GB.
Existing crashkernel= uses may no longer work, depending on where the
allocation falls. Option (2) above is a quick fix assuming that the
crashkernel reservation is small enough. What's a typical crashkernel
option here? That series is probably more prone to reservation failures.
Option (1), i.e. this series, doesn't solve the problem raised by
Bhupesh unless one uses the crashkernel=X,low argument. It can actually
make it worse even for ZONE_DMA32 since the allocation can go above 4G
(assuming that we change the ZONE_DMA configuration to only limit it to
1GB on RPi4).
I'm more inclined to keep the crashkernel= behaviour to ZONE_DMA
allocations. If this is too small for typical kdump, we can look into
expanding ZONE_DMA to 4G on non-RPi4 hardware (we had patches on the
list). In addition, if Chen thinks allocations above 4G are still needed
or if RPi4 needs a sufficiently large crashkernel=, I'd rather have a
",high" option to explicitly require such access.
[1] http://lists.infradead.org/pipermail/kexec/2020-July/020777.html
--
Catalin
