On 15/04/20 19:55, Sean Christopherson wrote: > Convert the exit_reason field in struct vcpu_vmx from a vanilla u32 to a > union, (ab)using the union to provide access to the basic exit reason and > flags. > > There is a fairly substantial delta relative to v1, as I ran with Vitaly's > suggestion to split nested_vmx_exit_reflected() into VM-Fail, "L0 wants" > and "L1 wants", and move the tracepoint into nested_vmx_reflect_vmexit(). > IMO, this yields cleaner and more understandable code overall, and helps > eliminate caching the basic exit reason (see below) by avoiding large > functions that repeatedly query the basic exit reason. The refactoring > isn't strictly related to making exit_reason a union, but the code would > conflict horribly and the end code nicely demonstrates the value of using > a union for the exit reason. > > There are three motivating factors for making exit_reason a union: > > - Help avoid bugs where a basic exit reason is compared against the full > exit reason, e.g. there have been two bugs where MCE_DURING_VMENTRY > was incorrectly compared against the full exit reason. > > - Clarify the intent of related flows, e.g. exit_reason is used for both > "basic exit reason" and "full exit reason", and it's not always clear > which of the two is intended without a fair bit of digging. > > - Prepare for future Intel features, e.g. SGX, that add new exit flags > that are less restricted than FAILED_VMENTRY, i.e. can be set on what > is otherwise a standard VM-Exit. > > v2: > - Don't snapshot the basic exit reason, i.e. either use vmx->exit_reason > directly or snapshot the whole thing. The resulting code is similar > to Xiaoyao's original patch, e.g. vmx_handle_exit() now uses > "exit_reason.basic" instead of "exit_reason" to reference the basic > exit reason. > - Split nested_vmx_exit_reflected() into VM-Fail, "L0 wants" and "L1 > wants", and move the tracepoint into nested_vmx_reflect_vmexit(). > [Vitaly] > - Use a "union vmx_exit_reason exit_reason" to handle a consistency > check VM-Exit on VM-Enter in nested_vmx_enter_non_root_mode() to avoid > some implicit casting shenanigans. [Vitaly] > - Collect tags. [Vitaly] > > v1: https://lkml.kernel.org/r/20200312184521.24579-1-sean.j.christopherson@xxxxxxxxx For now I committed only patches 1-9, just to limit the conflicts with the other series. I would like to understand how you think the conflicts should be fixed with the union. Paolo
