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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2025-02-06 02:55:21 +07:00
009bce1df0
Choo! Choo! All aboard the Split Lock Express, with direct service to
Wreckage!
Skip split_lock_verify_msr() if the CPU isn't whitelisted as a possible
SLD-enabled CPU model to avoid writing MSR_TEST_CTRL. MSR_TEST_CTRL
exists, and is writable, on many generations of CPUs. Writing the MSR,
even with '0', can result in bizarre, undocumented behavior.
This fixes a crash on Haswell when resuming from suspend with a live KVM
guest. Because APs use the standard SMP boot flow for resume, they will
go through split_lock_init() and the subsequent RDMSR/WRMSR sequence,
which runs even when sld_state==sld_off to ensure SLD is disabled. On
Haswell (at least, my Haswell), writing MSR_TEST_CTRL with '0' will
succeed and _may_ take the SMT _sibling_ out of VMX root mode.
When KVM has an active guest, KVM performs VMXON as part of CPU onlining
(see kvm_starting_cpu()). Because SMP boot is serialized, the resulting
flow is effectively:
on_each_ap_cpu() {
WRMSR(MSR_TEST_CTRL, 0)
VMXON
}
As a result, the WRMSR can disable VMX on a different CPU that has
already done VMXON. This ultimately results in a #UD on VMPTRLD when
KVM regains control and attempt run its vCPUs.
The above voodoo was confirmed by reworking KVM's VMXON flow to write
MSR_TEST_CTRL prior to VMXON, and to serialize the sequence as above.
Further verification of the insanity was done by redoing VMXON on all
APs after the initial WRMSR->VMXON sequence. The additional VMXON,
which should VM-Fail, occasionally succeeded, and also eliminated the
unexpected #UD on VMPTRLD.
The damage done by writing MSR_TEST_CTRL doesn't appear to be limited
to VMX, e.g. after suspend with an active KVM guest, subsequent reboots
almost always hang (even when fudging VMXON), a #UD on a random Jcc was
observed, suspend/resume stability is qualitatively poor, and so on and
so forth.
kernel BUG at arch/x86/kvm/x86.c:386!
CPU: 1 PID: 2592 Comm: CPU 6/KVM Tainted: G D
Hardware name: ASUS Q87M-E/Q87M-E, BIOS 1102 03/03/2014
RIP: 0010:kvm_spurious_fault+0xf/0x20
Call Trace:
vmx_vcpu_load_vmcs+0x1fb/0x2b0
vmx_vcpu_load+0x3e/0x160
kvm_arch_vcpu_load+0x48/0x260
finish_task_switch+0x140/0x260
__schedule+0x460/0x720
_cond_resched+0x2d/0x40
kvm_arch_vcpu_ioctl_run+0x82e/0x1ca0
kvm_vcpu_ioctl+0x363/0x5c0
ksys_ioctl+0x88/0xa0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x4c/0x170
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Fixes:
|
||
|---|---|---|
| .. | ||
| boot | ||
| configs | ||
| crypto | ||
| entry | ||
| events | ||
| hyperv | ||
| ia32 | ||
| include | ||
| kernel | ||
| kvm | ||
| lib | ||
| math-emu | ||
| mm | ||
| net | ||
| oprofile | ||
| pci | ||
| platform | ||
| power | ||
| purgatory | ||
| ras | ||
| realmode | ||
| tools | ||
| um | ||
| video | ||
| xen | ||
| .gitignore | ||
| Kbuild | ||
| Kconfig | ||
| Kconfig.assembler | ||
| Kconfig.cpu | ||
| Kconfig.debug | ||
| Makefile | ||
| Makefile_32.cpu | ||
| Makefile.um | ||