On Fri, Mar 11, 2022 at 11:29:23AM +0000, Liam Merwick wrote:
[ patch series targeting linux-5.4.y stable branch. ]
Creating a SEV-enabled guest with 380GB or more of memory causes a cpu soft-hang in the host running 5.4 with the following stacktrace:
kernel: watchdog: BUG: soft lockup - CPU#214 stuck for 22s! [qemu-kvm:6424] ... kernel: CPU: 214 PID: 6424 Comm: qemu-kvm Not tainted 5.4.183.stable #1 kernel: Hardware name: Oracle Corporation ORACLE SERVER E4-2c/Asm,MB Tray,2U,E4-2c, BIOS 78014000 01/05/2022 kernel: RIP: 0010:clflush_cache_range+0x35/0x40 kernel: Code: f0 0f b7 15 63 53 99 01 89 f6 48 89 d0 48 f7 d8 48 21 f8 48 01 f7 48 39 f8 73 0c 66 0f ae 38 48 01 d0 48 39 c7 77 f4 0f ae f0 <5d> c3 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 0f ae kernel: RSP: 0018:ffffacba5e98fc30 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13 kernel: RAX: ffffa1193cfbc000 RBX: ffffacbba4701000 RCX: 0000000000000000 kernel: RDX: 0000000000000040 RSI: 0000000000001000 RDI: ffffa1193cfbc000 kernel: RBP: ffffacba5e98fc30 R08: ffffacba5f44aca0 R09: ffffacbac3701000 kernel: R10: 0000000000000080 R11: ffff9f8500000af0 R12: ffffa18074a22f80 kernel: R13: ffffacbaf6889dd8 R14: ffffacba5f41d960 R15: ffffacba5f44aca0 kernel: FS: 00007fbe04321f00(0000) GS:ffffa1814ed80000(0000) knlGS:0000000000000000 kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 kernel: CR2: 00007dfbebd7d000 CR3: 000801fb93d68002 CR4: 0000000000760ee0 kernel: PKRU: 55555554 kernel: Call Trace: kernel: sev_clflush_pages.part.56+0x50/0x70 [kvm_amd] kernel: svm_register_enc_region+0xe2/0x120 [kvm_amd] kernel: kvm_arch_vm_ioctl+0x524/0xbd0 [kvm] kernel: ? release_pages+0x212/0x430 kernel: ? __pagevec_lru_add_fn+0x192/0x2f0 kernel: kvm_vm_ioctl+0x9c/0x9d0 [kvm] kernel: ? __lru_cache_add+0x59/0x70 kernel: ? lru_cache_add_active_or_unevictable+0x39/0xb0 kernel: ? __handle_mm_fault+0xa74/0xfd0 kernel: ? __switch_to_asm+0x34/0x70 kernel: do_vfs_ioctl+0xa9/0x640 kernel: ? __audit_syscall_entry+0xdd/0x130 kernel: ksys_ioctl+0x67/0x90 kernel: __x64_sys_ioctl+0x1a/0x20 kernel: do_syscall_64+0x60/0x1d0 kernel: entry_SYSCALL_64_after_hwframe+0x44/0xa9 kernel: RIP: 0033:0x7fbe0086563b kernel: Code: 0f 1e fa 48 8b 05 4d b8 2c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 1d b8 2c 00 f7 d8 64 89 01 48 kernel: RSP: 002b:00007ffedf577418 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 kernel: RAX: ffffffffffffffda RBX: 00007dfbebe00000 RCX: 00007fbe0086563b kernel: RDX: 00007ffedf577490 RSI: ffffffff8010aebb RDI: 000000000000000d kernel: RBP: 000001c200000000 R08: ffffffffffffffff R09: ffffffffffffffff kernel: R10: ffffffffffffffff R11: 0000000000000246 R12: 000001c200000000 kernel: R13: 00007dfbebe00000 R14: 0000000000000000 R15: 0000000000000000
The problem is the time spent flushing the caches when pinning memory for SEV but it's unnecessary as it turns out - it is resolved by backporting the following commits from Linux 5.10
e1ebb2b49048 KVM: SVM: Don't flush cache if hardware enforces cache coherency across encryption domains (conflict due to the function it fixed being moved in a refactoring in 5.7).
along with 3 other commits needed as dependencies. (fbd5969d1ff2 avoids a conflict in 5866e9205b47)
fbd5969d1ff2 x86/cpufeatures: Mark two free bits in word 3 5866e9205b47 x86/cpu: Add hardware-enforced cache coherency as a CPUID feature 75d1cc0e05af x86/mm/pat: Don't flush cache if hardware enforces cache coherency across encryption domnains
Tested by creating various sized guests up to 1.8TB, with and without SEV enabled, running a few benchmarks and passing kvm-unit-tests.
Borislav Petkov (1): x86/cpufeatures: Mark two free bits in word 3
Krish Sadhukhan (3): x86/cpu: Add hardware-enforced cache coherency as a CPUID feature x86/mm/pat: Don't flush cache if hardware enforces cache coherency across encryption domnains KVM: SVM: Don't flush cache if hardware enforces cache coherency across encryption domains
arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/kernel/cpu/scattered.c | 1 + arch/x86/kvm/svm.c | 3 ++- arch/x86/mm/pageattr.c | 2 +- 4 files changed, 6 insertions(+), 2 deletions(-)
-- 2.27.0
All now queued up, thanks!
greg k-h