Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 9 Jan 2024 16:19:02 -0600 | Subject | Re: [PATCH v1 15/26] x86/sev: Introduce snp leaked pages list | From | "Kalra, Ashish" <> |
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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@amd.com> >> >> 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@amd.com> >> [mdr: relocate to arch/x86/virt/svm/sev.c] >> Signed-off-by: Michael Roth <michael.roth@amd.com> > 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@amd.com/ > 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
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