Hello Vlastimil,
On 1/8/2024 4:45 AM, Vlastimil Babka wrote:
On 12/30/23 17:19, Michael Roth wrote:
From: Ashish Kalra <ashish.kalra@xxxxxxx>
Pages are unsafe to be released back to the page-allocator, if they
have been transitioned to firmware/guest state and can't be reclaimed
or transitioned back to hypervisor/shared state. In this case add
them to an internal leaked pages list to ensure that they are not freed
or touched/accessed to cause fatal page faults.
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
[mdr: relocate to arch/x86/virt/svm/sev.c]
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
Hi, sorry I didn't respond in time to the last mail discussing previous
version in
https://lore.kernel.org/all/8c1fd8da-912a-a9ce-9547-107ba8a450fc@xxxxxxx/
due to upcoming holidays.
I would rather avoid the approach of allocating container objects:
- it's allocating memory when effectively losing memory, a dangerous thing
- are all the callers and their context ok with GFP_KERNEL?
- GFP_KERNEL_ACCOUNT seems wrong, why would we be charging this to the
current process, it's probably not its fault the pages are leaked? Also the
charging can fail?
- given the benefit of having leaked pages on a list is basically just
debugging (i.e. crash dump or drgn inspection) this seems too heavy
I think it would be better and sufficient to use page->lru for order-0 and
head pages, and simply skip tail pages (possibly with adjusted warning
message for that case).
Vlastimil
<snip
Considering the above thoughts, this is updated version of
snp_leak_pages(), looking forward to any review comments/feedback you
have on the same:
void snp_leak_pages(u64 pfn, unsigned int npages)
{
struct page *page = pfn_to_page(pfn);
pr_debug("%s: leaking PFN range 0x%llx-0x%llx\n", __func__,
pfn, pfn + npages);
spin_lock(&snp_leaked_pages_list_lock);
while (npages--) {
/*
* Reuse the page's buddy list for chaining into the leaked
* pages list. This page should not be on a free list
currently
* and is also unsafe to be added to a free list.
*/
if ((likely(!PageCompound(page))) || (PageCompound(page) &&
!PageTail(page) && compound_head(page) == page))
/*
* Skip inserting tail pages of compound page as
* page->buddy_list of tail pages is not usable.
*/
list_add_tail(&page->buddy_list,
&snp_leaked_pages_list);
sev_dump_rmpentry(pfn);
snp_nr_leaked_pages++;
pfn++;
page++;
}
spin_unlock(&snp_leaked_pages_list_lock);
}
Thanks, Ashish
