Re: [Xen-devel] [PATCH]: Fix Xen domU boot with batched mprotect

From: Jan Beulich
Date: Fri Oct 17 2008 - 11:30:10 EST

>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 17.10.08 17:19 >>>
>Jan Beulich wrote:
>>>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 16.10.08 18:10 >>>
>>> The current x86-64 implementation is:
>>> bool __virt_addr_valid(unsigned long x)
>>> {
>>> if (x >= __START_KERNEL_map) {
>>> x -= __START_KERNEL_map;
>>> if (x >= KERNEL_IMAGE_SIZE)
>>> return false;
>> This, imo, is still broken (i.e. the name of the function still isn't matched
>> by the implementation): KERNEL_IMAGE_SIZE is a constant and doesn't
>> account for the fact that only the real kernel image can be relied upon
>> to be mapped.
>Perhaps, but I don't think it matters too much. Unless you have a tiny
>amount of physical memory, locations in the kernel mapping beyond the
>actual kernel will still resolve to proper locations in the linear map.

Is e.g. 256Mb tiny? KERNEL_IMAGE_SIZE these days is 512Mb... Indeed,
when it was 40Mb (up until a few releases ago), this indeed wouldn't


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