On 11/03/2015 05:59 PM, Paolo Bonzini wrote:
On 03/11/2015 06:49, Kai Huang wrote:
I found PML was broken since below commit:
commit feda805fe7c4ed9cf78158e73b1218752e3b4314
Author: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
Date: Wed Sep 9 14:05:55 2015 +0800
KVM: VMX: unify SECONDARY_VM_EXEC_CONTROL update
Unify the update in vmx_cpuid_update()
Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
[Rewrite to use vmcs_set_secondary_exec_control. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
The reason is PML after above commit vmx_cpuid_update calls
vmx_secondary_exec_control, in which PML is disabled unconditionally, as PML is
enabled in creating vcpu. Therefore if vcpu_cpuid_update is called after vcpu is
created, PML will be disabled unexpectedly while log-dirty code still think PML
is used. Actually looks calling vmx_secondary_exec_control in vmx_cpuid_update
is likely to break any VMX features that is enabled/disabled on demand by
updating SECONDARY_VM_EXEC_CONTROL, if vmx_cpuid_update is called between the
feature is enabled and disabled.
Fix this by calling vmcs_read32 to read out SECONDARY_VM_EXEC_CONTROL directly.
vmx_cpuid_update() is meant to be mostly idempotent; the parts that
depend on the current VMCS configuration are hidden in
vmcs_set_secondary_control. So a better fix would be to add
SECONDARY_EXEC_ENABLE_PML to vmcs_set_secondary_exec_control's
"mask" variable. However, you can see from the comment:
/*
* These bits in the secondary execution controls field
* are dynamic, the others are mostly based on the hypervisor
* architecture and the guest's CPUID. Do not touch the
* dynamic bits.
*/
that even this is not the optimal fix. SECONDARY_EXEC_ENABLE_PML is
either always set or always clear, so it shouldn't be in "mask".
Instead, it should be in vmcs_config.cpu_based_2nd_exec_ctrl. It isn't
because my review didn't notice this remnant of your original
implementation, which dynamically enabled/disabled PML.
In fact, cpu_has_vmx_pml() expects SECONDARY_EXEC_ENABLE_PML to be set
in vmcs_config.cpu_based_2nd_exec_ctrl, so it is a bit confusing to
remove the bit unconditionally in vmx_secondary_exec_control!
So I think SECONDARY_EXEC_ENABLE_PML should not be removed unconditionally
from exec_control in vmx_secondary_exec_control; the removal should be
conditional on !enable_pml, like we do for e.g. EPT or VPID. If you do this,
vmx_enable_pml and vmx_disable_pml need not touch SECONDARY_VM_EXEC_CONTROL
anymore. Do you agree? If so, can you prepare a patch along these lines?
Thanks Paolo for your comments.
Sure I agree. I will send out the v2 patch by following what you suggested.
(Since you are at it, perhaps you can rename vmx_enable_pml and
vmx_disable_pml, since they will only allocate and free the PML page).
I intend to rename vmx_enable{disable}_pml to
vmx_create{destroy}_pml_buffer, as besides allocating buffer, we also
need to write buffer address and PML index to VMCS.
Thanks,
-Kai
Thanks for reporting the issue!
Paolo
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