During the last kvm forum, I described a unit test framework that can
help test the kvm APIs. Briefly, it starts a process in host userspace,
which sets up a memory slot mapping gpa 0:3G to hva 0:3G. It then sets
up guest registers for unpaged protected mode (or paged protected mode
with 1:1 mapping). The effect is that we have a 1:1 gva->hva
translation, and can use KVM_RUN to run host code in guest mode.
There is a snag however. kvm calls get_user_pages_fast(.write = 1), and
the host process maps its code pages read-only.
The way I'd like to work around this is to map read-only accesses to
read-only pages as read-only. This also prevents ksm cow pages from
being broken by read accesses. It can also be used to get the page size
for transparent huge pages (and later hugetlbfs too).
So, for a read fault we do:
pte_t pte;
get_user_pages_ptes_fast(..., page, &pte, 1, .write = 0)
...
if (pte_transhuge(pte)) // or however it's called
...
...
if (pte_write(pte))
map writeable
else
map readonly
Any snags? or alternatives?
--
error compiling committee.c: too many arguments to function
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