Messages in this thread | | | Subject | Re: SEV guest regression in 4.18 | From | Brijesh Singh <> | Date | Tue, 21 Aug 2018 11:07:38 -0500 |
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On 08/21/2018 10:19 AM, Borislav Petkov wrote: > On Tue, Aug 21, 2018 at 09:37:56AM -0500, Brijesh Singh wrote: >> Those variables are accessed immediately by the tsc calibration code >> path hence we will not able to delay the allocation. > > If you mean, check_tsc_sync_source/_target(), those are called pretty > late, AFAICT. > > And I see a setup_arch() -> init_mem_mapping -> ... -> > kernel_physical_mapping_init() call which happens much earlier. > > Again, AFAICT. You probably should try it though, to make sure. >
Here is a typical flow:
setup_arch() ....
init_hypervisor_platform() kvmclock_init() kvm_register_clock("primary cpu clock") /* this shares the physical address of variable with HV. * Ideally you want C-bit to be cleared before we give * the address to HV because HV may start using the * variable as soon as we issue wrmsrl(MSR_KVM_SYSTEM_TIME). * * we may able to relax rules that variable should be mapped * with C=0 before making the wrmsrl(). Since HV will anyways * write the data with C=0. The important thing is when guest * tries to read it must map the address as C=0. */ Later part of kvmclock_init provides a hooks for tsc calibration
tsc_early_init() determine_cpu_tsc_frequencies() /* this will call tsc calibration hooks registered by the * kvmclock_init. The hooks basically reads those variables. * These variable must be mapped with C=0 otherwise we will * not be able to get the data written by the hypervisor. */
... ... ... ...
trim_low_memory_range init_mem_mapping()
...
The tsc_early_init() is called before setup_arch() -> init_mem_mapping.
-Brijesh
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