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Reword the comment to better describe what I found while researching the

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problem that led to this temporary workaround (and also so I can properly
cite the PR in the commit this time).

In general this is intended to be a temporary workaround until we can figure
out why including any ram from the last megabyte of the physical address
space leads to a NULL pointer deref.  Debugging that is made trickier by the
fact that I couldn't even get a backtrace in ddb.

PR:		201614
This commit is contained in:
Ian Lepore 2016-01-02 23:14:52 +00:00
parent 24bbe7a40c
commit 9df1d85ebb
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=293065
1 changed files with 6 additions and 8 deletions
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14
sys/arm/arm/physmem.c
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@ -282,16 +282,14 @@ arm_physmem_hardware_region(vm_paddr_t pa, vm_size_t sz)
* pmap_extract() == 0 means failure.
*
* Also filter out the page at the end of the physical address space --
* if addr is non-zero and addr+size is zero that means we wrapped to
* the next byte beyond what vm_paddr_t can express. The calculations
* in vm_page_startup() are going to have the same problem, so just work
* around it by leaving the last page out.
* if addr is non-zero and addr+size is zero we wrapped to the next byte
* beyond what vm_paddr_t can express. That leads to a NULL pointer
* deref early in startup; work around it by leaving the last page out.
*
* XXX This just in: subtract out a whole megabyte, not just 1 page.
* Reducing the size by anything less than 1MB results in a NULL pointer
* deref in _vm_map_lock_read() very early in startup. Better to give
* up a whole megabyte than leave some folks with an unusable system
* while we investigate.
* Reducing the size by anything less than 1MB results in the NULL
* pointer deref in _vm_map_lock_read(). Better to give up a megabyte
* than leave some folks with an unusable system while we investigate.
*/
if (pa == 0) {
pa = PAGE_SIZE;