Thanks.
在 2022/7/6 23:40, Catalin Marinas 写道:
On Wed, Jul 06, 2022 at 11:18:22PM +0800, guanghui.fgh wrote:
在 2022/7/6 21:54, Mike Rapoport 写道:
One thing I can think of is to only remap the crash kernel memory if it is
a part of an allocation that exactly fits into one ore more PUDs.
Say, in reserve_crashkernel() we try the memblock_phys_alloc() with
PUD_SIZE as alignment and size rounded up to PUD_SIZE. If this allocation
succeeds, we remap the entire area that now contains only memory allocated
in reserve_crashkernel() and free the extra memory after remapping is done.
If the large allocation fails, we fall back to the original size and
alignment and don't allow unmapping crash kernel memory in
arch_kexec_protect_crashkres().
There is a new method.
I think we should use the patch v3(similar but need add some changes)
1.We can walk crashkernle block/section pagetable,
[[[(keep the origin block/section mapping valid]]]
rebuild the pte level page mapping for the crashkernel mem
rebuild left & right margin mem(which is in same block/section mapping but
out of crashkernel mem) with block/section mapping
2.'replace' the origin block/section mapping by new builded mapping
iterately
With this method, all the mem mapping keep valid all the time.
As I already commented on one of your previous patches, this is not
allowed by the architecture. If FEAT_BBM is implemented (ARMv8.4 I
think), the worst that can happen is a TLB conflict abort and the
handler should invalidate the TLBs and restart the faulting instruction,
assuming the handler won't try to access the same conflicting virtual
address. Prior to FEAT_BBM, that's not possible as the architecture does
not describe a precise behaviour of conflicting TLB entries (you might
as well get the TLB output of multiple entries being or'ed together).
I think there is another way to handle it.
1.We can rebuild the crashkernel mem mapping firstly,
but [[[don't change the origin linear mapping]]].
2.Afterward, we can reuse the idmap_pg_dir and switch to it.
We use idmap_pg_dir to change the linear mapping which complyes with the
TLB BBM.
