x86/setup: Do not reserve crashkernel high memory if low reservation failed

People reported that when allocating crashkernel memory using
the ",high" and ",low" syntax, there were cases where the
reservation of the high portion succeeds but the reservation of
the low portion fails.

Then kexec can load the kdump kernel successfully, but booting
the kdump kernel fails as there's no low memory.

The low memory allocation for the kdump kernel can fail on large
systems for a couple of reasons. For example, the manually
specified crashkernel low memory can be too large and thus no
adequate memblock region would be found.

Therefore, we try to reserve low memory for the crash kernel
*after* the high memory portion has been allocated. If that
fails, we free crashkernel high memory too and return. The user
can then take measures accordingly.

Tested-by: Joerg Roedel <[email protected]>
Signed-off-by: Baoquan He <[email protected]>
[ Massage text. ]
Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Joerg Roedel <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Young <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mark Salter <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: WANG Chao <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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