cpuid_pass2 incorrectly asserts when disabling xsave
When bogus xsave information is encountered -- generally from a hypervisor that has disabled xsave support in a more curious way, such as on Amazon or VMware, we end up blowing an ASSERT when more than one CPU exists:
WARNING: cpu1: CPUID.0xD returns invalid value: hw_low = 0, hw_high = 0, xsave_size = 832, ymm_size = 0, ymm_offset = 0 panic[cpu1]/thread=ffffff00396aac40: assertion failed: cpu->cpu_id == 0, file: ../../i86pc/os/cpuid.c, line: 1951 Warning - stack not written to the dump buffer ffffff00396aab40 genunix:process_type+17b920 () ffffff00396aabd0 unix:cpuid_pass2+726 () ffffff00396aac20 unix:mp_startup_common+1f8 () ffffff00396aac30 unix:mp_startup_boot+e () >> warning! 8-byte aligned %fp = ffffff00396aac28 ffffff00396aac28 0 () >> mis-aligned %fp = fffffffffb83985e syncing file systems... done skipping system dump - no dump device configured rebooting...
Importantly here the ASSERT that we blew was asserting that our current CPU was CPU0. In particular, this is the code path that is trying to disable xsave support. However, if we have multiple CPUs, we'll always end up down this code path that is trying to disable xsave support and blow the assertion. Most folks don't normally see this as they're not using debug bits.
The fix here is straightforward, rather than ASSERTing on the CPU, we need to turn that into a branch and if we're in the CPU 0 path, we'll disable xsave support and if we're in the non-CPU0 path we need to assert that it's already been disabled.
Updated by Electric Monk almost 7 years ago
- Status changed from New to Closed
- % Done changed from 90 to 100
commit dcf050af29bc1c6bd38ba7f173dc18bb7c5629e1 Author: Robert Mustacchi <email@example.com> Date: 2014-09-25T02:11:36.000Z 5192 cpuid_pass2 incorrectly asserts when disabling xsave Reviewed by: Richard Lowe <firstname.lastname@example.org> Reviewed by: Hans Rosenfeld <email@example.com> Reviewed by: Garrett D'Amore <firstname.lastname@example.org> Reviewed by: Josef 'Jeff' Sipek <email@example.com> Approved by: Gordon Ross <firstname.lastname@example.org>