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Re: [PATCH 3/3] i386: Make sure kvm_arch_set_tsc_khz() succeeds on migra


From: Paolo Bonzini
Subject: Re: [PATCH 3/3] i386: Make sure kvm_arch_set_tsc_khz() succeeds on migration when 'hv-reenlightenment' was exposed
Date: Fri, 19 Mar 2021 12:04:13 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0

On 19/03/21 10:41, Vitaly Kuznetsov wrote:
What I want to achieve is to forbid migration of VMs with
reenlightenment, if they don't also specify tsc-khz to the frequency of
the TSC on the source host.  We can't check it at the beginning of
migration, but at least we can check it at the end.

Maybe we're talking about two different things?
No, your suggestion basically extends mine and I'm just trying to
understand the benefit. With my suggestion, it is not required to
specify tsc-khz on the source, we just take 'native' tsc frequency as a
reference. Post-migration, we require that KVM_SET_TSC_KHZ succeeds (and
not just 'try' like kvm_arch_put_registers() does so we effectively
break migration when we are unable to set the desired TSC frequency
(also at the end).

Oh, okay, I understand the confusion; I was thinking of checking for user_tsc_khz in the post-load function for reenlightenment, not in the command line processing.

Paolo




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