Messages in this thread |  | | Subject | Re: Re: [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime handler | From | Bo Gan <> | Date | Wed, 22 Apr 2020 18:33:13 -0700 |
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On 4/15/20 8:53 AM, Joerg Roedel wrote: > Hi Mike, > > On Tue, Apr 14, 2020 at 07:03:44PM +0000, Mike Stunes wrote: >> set_memory_decrypted needs to check the return value. I see it >> consistently return ENOMEM. I've traced that back to split_large_page >> in arch/x86/mm/pat/set_memory.c. > > I agree that the return code needs to be checked. But I wonder why this > happens. The split_large_page() function returns -ENOMEM when > alloc_pages() fails. Do you boot the guest with minal RAM assigned? > > Regards, > > Joerg >
I just want to add some context around this. The call path that lead to the failure is like the following:
__alloc_pages_slowpath __alloc_pages_nodemask alloc_pages_current alloc_pages split_large_page __change_page_attr __change_page_attr_set_clr __set_memory_enc_dec set_memory_decrypted sev_es_init_ghcbs trap_init -> before mm_init (in init/main.c) start_kernel x86_64_start_reservations x86_64_start_kernel secondary_startup_64
At this time, mem_init hasn't been called yet (which would be called by mm_init). Thus, the free pages are still owned by memblock. It's in mem_init (x86/mm/init_64.c) that memblock_free_all gets called and free pages are released.
During testing, I've also noticed that debug_pagealloc=1 will make the issue disappear. That's because with debug_pagealloc=1, probe_page_size_mask in x86/mm/init.c will not allow large pages (2M/1G). Therefore, no split_large_page would happen. Similarly, if CPU doesn't have X86_FEATURE_PSE, there won't be large pages either.
Any thoughts? Maybe split_large_page should get pages from memblock at early boot?
Bo
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