Messages in this thread | | | Subject | Re: [PATCH 1/2] kvm: vmx: Use basic exit reason to check if it's the specific VM EXIT | From | Xiaoyao Li <> | Date | Thu, 27 Feb 2020 16:35:20 +0800 |
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On 2/27/2020 7:59 AM, Sean Christopherson wrote: > On Tue, Feb 25, 2020 at 02:41:20PM +0800, Xiaoyao Li wrote: >> On 2/25/2020 2:13 PM, Sean Christopherson wrote: >>> On Tue, Feb 25, 2020 at 08:13:15AM +0800, Xiaoyao Li wrote: >>>> On 2/25/2020 12:17 AM, Sean Christopherson wrote: >>>> I have thought about union, but it seems >>>> >>>> union { >>>> u16 exit_reason; >>>> u32 full_exit_reason; >>>> } >>>> >>>> is not a good name. Since there are many codes in vmx.c and nested.c assume >>>> that exit_reason stands for 32-bit EXIT REASON vmcs field as well as >>>> evmcs->vm_exit_reason and vmcs12->vm_exit_reason. Do we really want to also >>>> rename them to full_exit_reason? >>> >>> It's actually the opposite, almost all of the VMX code assumes exit_reason >>> holds only the basic exit reason, i.e. a 16-bit value. For example, SGX >>> adds a modifier flag to denote a VM-Exit was from enclave mode, and that >>> bit needs to be stripped from exit_reason, otherwise all the checks like >>> "if (exit_reason == blah_blah_blah)" fail. >>> >>> Making exit_reason a 16-bit alias of the full/extended exit_reason neatly >>> sidesteps that issue. And it is an issue that has caused actual problems >>> in the past, e.g. see commit beb8d93b3e42 ("KVM: VMX: Fix handling of #MC >>> that occurs during VM-Entry"). Coincidentally, that commit also removes a >>> local "u16 basic_exit_reason" :-). >>> >>> Except for one mistake, the pseudo-patch below is the entirety of required >>> changes. Most (all?) of the functions that take "u32 exit_reason" can (and >>> should) continue to take a u32. >>> >>> As for the name, I strongly prefer keeping the exit_reason name for the >>> basic exit reason. The vast majority of VM-Exits do not have modifiers >>> set, i.e. "basic exit reason" == vmcs.EXIT_REASON for nearly all normal >>> usage. This holds true in every form of communication, e.g. when discussing >>> VM-Exit reasons, it's never qualified with "basic", it's simply the exit >>> reason. IMO the code is better off following the colloquial usage of "exit >>> reason". A simple comment above the union would suffice to clear up any >>> confusion with respect to the SDM. >> >> Well, for this reason we can keep exit_reason for 16-bit usage, and define >> full/extended_exit_reason for 32-bit cases. This makes less code churn. >> >> But after we choose to use exit_reason and full/extended_exit_reason, what >> if someday new modifier flags are added and we want to enable some modifier >> flags for nested case? >> I guess we need to change existing exit_reason to full/extended_exit_reason >> in nested.c/nested.h to keep the naming rule consistent. > > Ah, good point. But, that's just another bug in my psuedo patch :-) > It's literally one call site that needs to be updated. E.g. > > if (is_guest_mode(vcpu) && nested_vmx_exit_reflected(vcpu, exit_reason)) > return nested_vmx_reflect_vmexit(vcpu, full_exit_reason); >
shouldn't we also pass full_exit_reason to nested_vmx_exit_reflected()?
> Everywhere else KVM calls nested_vmx_reflect_vmexit() is (currently) done
I guess you wanted to say nested_vmx_vmexit() not nested_vmx_reflect_vmexit() here.
> with a hardcoded value (except handle_vmfunc(), but I actually want to > change that one). >
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