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Handle overflow in calculating max kmem size.

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vm_kmem_size is u_long, and it might be not capable of holding page
count times PAGE_SIZE, even when scaled down by VM_KMEM_SIZE_SCALE.  As
bde reported, 12G PAE config ends up with zero for kmem size.

Explicitly check for overflow and clamp kmem size at vm_kmem_size_max.
If we end up at zero size because VM_KMEM_SIZE_MAX is not defined,
panic with clear explanation rather then failing in a way which is
hard to relate.

Reported by:	bde, pho
Tested by:	pho
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D18767
This commit is contained in:
Konstantin Belousov 2019-01-14 07:31:19 +00:00
parent 40343be5a1
commit 28b740da38
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=343017
1 changed files with 5 additions and 2 deletions
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7
sys/kern/kern_malloc.c
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@ -920,13 +920,16 @@ kmeminit(void)
* variable:
*/
if (vm_kmem_size == 0) {
vm_kmem_size = (mem_size / vm_kmem_size_scale) * PAGE_SIZE;
vm_kmem_size = mem_size / vm_kmem_size_scale;
vm_kmem_size = vm_kmem_size * PAGE_SIZE < vm_kmem_size ?
vm_kmem_size_max : vm_kmem_size * PAGE_SIZE;
if (vm_kmem_size_min > 0 && vm_kmem_size < vm_kmem_size_min)
vm_kmem_size = vm_kmem_size_min;
if (vm_kmem_size_max > 0 && vm_kmem_size >= vm_kmem_size_max)
vm_kmem_size = vm_kmem_size_max;
}
if (vm_kmem_size == 0)
panic("Tune VM_KMEM_SIZE_* for the platform");
/*
* The amount of KVA space that is preallocated to the