On Wed, 3 Feb 2021 00:41:00 +0200 Jarkko Sakkinen wrote: > On Wed, Feb 03, 2021 at 08:23:40AM +1300, Kai Huang wrote: > > On Tue, 2 Feb 2021 19:24:42 +0200 Jarkko Sakkinen wrote: > > > On Mon, Feb 01, 2021 at 01:32:59PM +1300, Kai Huang wrote: > > > > On Sat, 30 Jan 2021 17:00:46 +0200 Jarkko Sakkinen wrote: > > > > > On Tue, Jan 26, 2021 at 10:31:37PM +1300, Kai Huang wrote: > > > > > > From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > > > > > > > > > > > > Convert vcpu_vmx.exit_reason from a u32 to a union (of size u32). The > > > > > > full VM_EXIT_REASON field is comprised of a 16-bit basic exit reason in > > > > > > bits 15:0, and single-bit modifiers in bits 31:16. > > > > > > > > > > > > Historically, KVM has only had to worry about handling the "failed > > > > > > VM-Entry" modifier, which could only be set in very specific flows and > > > > > > required dedicated handling. I.e. manually stripping the FAILED_VMENTRY > > > > > > bit was a somewhat viable approach. But even with only a single bit to > > > > > > worry about, KVM has had several bugs related to comparing a basic exit > > > > > > reason against the full exit reason store in vcpu_vmx. > > > > > > > > > > > > Upcoming Intel features, e.g. SGX, will add new modifier bits that can > > > > > > BTW, SGX is not an upcoming CPU feature. > > > > Probably Sean was implying: "Upcoming CPU features that will be supported by > > Linux". I don't see big deal here. > > > > > > > > Also, broadly speaking of upcoming features is not right thing to do. > > > Better just to scope this down SGX. Theoretically upcoming CPU features > > > can do pretty much anything. This is change is first and foremost done > > > for SGX. > > > > > > > > > be set on more or less any VM-Exit, as opposed to the significantly more > > > > > > restricted FAILED_VMENTRY, i.e. correctly handling everything in one-off > > > > > > flows isn't scalable. Tracking exit reason in a union forces code to > > > > > > explicitly choose between consuming the full exit reason and the basic > > > > > > exit, and is a convenient way to document and access the modifiers. > > > > > > > > > > I *believe* that the change is correct but I dropped in the last paragraph > > > > > - most likely only because of lack of expertise in this area. > > > > > > > > > > I ask the most basic question: why SGX will add new modifier bits? > > > > > > > > Not 100% sure about your question. Assuming you are asking SGX hardware > > > > behavior, SGX architecture adds a new modifier bit (27) to Exit Reason, similar > > > > to new #PF.SGX bit. > > > > > > > > Please refer to SDM Volume 3, Chapter 27.2.1 Basic VM-Exit Information. > > > > > > > > Sean's commit msg already provides significant motivation of the change in this > > > > patch. > > > > > > Just describe why SGX requires this. That's all. > > > > This patch is to change vmexit info from u32 to union, because at least one > > additional modifier is going to be added, due to SGX. So the motivation of this > > patch is the fact that "one or more additional modifier bits will be added", > > and SGX is just example. > > > > So I don't think adding too much SGX backgroud in *THIS* patch is needed. > > And another patch: > > > > [RFC PATCH v3 21/27] KVM: VMX: Add basic handling of VM-Exit from SGX enclave > > > > already has enough information of "why new modifier bit is aadded for SGX". > > Sean also replied to you. > > Well it comes after this patch. So you either need to provide the context > here or reorder patches. If latter is impossible, I would just add those > couple of paragraphs that Sean wrote. As I explained, to me the motivation of this patch is due to "adding additional modifier bit", but not due to "adding additional modifier bit *due to SGX*". For instance, let's remove SGX in the commit msg, this patch still stands. Correct? Sean's paragraph is about why *SGX* adds one additional modifier bit, which needs to be in another patch, and logically, that patch comes later. > > > Please look at that patch and see whether it satisfies you. > > Well there needs to be causality in patches. I should be able to review > the patches if 17-> did not exist. > > > > > > > > > > /Jarkko > > > > /Jarkko
