Messages in this thread | | | From | Brijesh Singh <> | Subject | SEV guest regression in 4.18 | Date | Mon, 20 Aug 2018 17:11:53 -0500 |
| |
Hi All,
The following commit
" x86/kvmclock: Remove memblock dependency
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=368a540e0232ad446931f5a4e8a5e06f69f21343
" broke the SEV support in 4.18.
Since the guest physical address holding the wall_clock and vcpu_time_info are shared with the hypervisor it must be mapped as "decrypted" when SEV is active. To clear the C-bit we use kernel_physical_mapping_init() to split the large pages into 4K before changing the C-bit. Now the kernel_physical_mapping_init() is failing to allocate the memory because its called very early.
[ 0.000000] Call Trace: [ 0.000000] ? dump_stack+0x5c/0x80 [ 0.000000] ? panic+0xe7/0x247 [ 0.000000] ? alloc_low_pages+0x130/0x130 [ 0.000000] ? kernel_physical_mapping_init+0xe0/0x204 [ 0.000000] ? early_set_memory_enc_dec+0x123/0x174 [ 0.000000] ? 0xffffffffae000000 [ 0.000000] ? kvmclock_init+0x60/0x1ea [ 0.000000] ? kvm_init_platform+0xa/0x16 [ 0.000000] ? setup_arch+0x434/0xce9 [ 0.000000] ? start_kernel+0x67/0x52e [ 0.000000] ? load_ucode_bsp+0x76/0x12e [ 0.000000] ? secondary_startup_64+0xa4/0xb0
I don't have proper solution to fix it. I have the following two approaches in mind:
1) - reserve a few pages in head_64.S - pass a flag in kernel_physical_mapping_init() to tell it to use the preallocated pages instead of alloc_low_pages().
or
2) - update hv_clock_boot and hv_clock_boot to align PMD_SIZE - when variables are PMD_SIZE aligned then we do not need to split the pages hence avoid the allocation issue.
Since the variables are static hence we also need to update the contents to match with updated C-bit. Currently, we use sme_early_decrypt() to perform in-place decrypt but this routines can not be called before pat_init() hence we probably need to do come up with some other approach for this as well.
Any suggestions/recommendations ?
Thanks Brijesh
| |