于 2012年10月15日 23:43, Avi Kivity 写道: > On 10/12/2012 08:40 AM, Zhang Yanfei wrote: >> Currently, kdump just makes all the logical processors leave VMX operation by >> executing VMXOFF instruction, so any VMCSs active on the logical processors >> may >> be corrupted. But, sometimes, we need the VMCSs to debug guest images >> contained >> in the host vmcore. To prevent the corruption, we should VMCLEAR the VMCSs >> before >> executing the VMXOFF instruction. > > How have you verified that VMXOFF doesn't flush cached VMCSs already? >
I tried some tests, for example, I made copies for every vmcs, and in the kdump path, I backed up all the loaded vmcs into the copies before vmxoff. After generating the vmcore, I retrieve the vmcss and their copies, and compare them, no differences. Another test is using VMCLEAR to clear all the loaded vmcs before VMXOFF, and compare the vmcss and their copies, there are indeed differences between the vmcs and its copy. I know the tests may be not so convincing, for example, I used memcpy to back up the vmcss and it is an ordinary memory operation. But to ensure the non-corruption of the vmcss in the vmcore, I think we should VMCLEAR the vmcss before VMXOFF just as the Intel spec says. >> >> The patch set provides an alternative way to clear VMCSs related to guests >> on all cpus when host is doing kdump. >> > > I'm not sure the sysctl is really necessary. The only reason to turn if > off is if the corruption is so severe that the loaded vmcs list itself > causes a crash. I think it should be rare enough that we can do it > unconditionally. > You mean not using sysctl and just let VMCLEAR-VMCSS be a default behaviour? If so, I agree with you. Thanks Zhang Yanfei -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
