On Mon, 2022-01-31 at 15:56 +0100, Paolo Bonzini wrote: > On 1/28/22 16:42, Sean Christopherson wrote: > > On Fri, Jan 28, 2022, Paolo Bonzini wrote: > > > On 1/28/22 01:51, Sean Christopherson wrote: > > > > Drop KVM_X86_OP_NULL, which is superfluous and confusing. The macro is > > > > just a "pass-through" to KVM_X86_OP; it was added with the intent of > > > > actually using it in the future, but that obviously never happened. The > > > > name is confusing because its intended use was to provide a way for > > > > vendor implementations to specify a NULL pointer, and even if it were > > > > used, wouldn't necessarily be synonymous with declaring a kvm_x86_op as > > > > DEFINE_STATIC_CALL_NULL. > > > > > > > > Lastly, actually using KVM_X86_OP_NULL as intended isn't a maintanable > > > > approach, e.g. bleeds vendor details into common x86 code, and would > > > > either be prone to bit rot or would require modifying common x86 code > > > > when modifying a vendor implementation. > > > > > > I have some patches that redefine KVM_X86_OP_NULL as "must be used with > > > static_call_cond". That's a more interesting definition, as it can be used > > > to WARN if KVM_X86_OP is used with a NULL function pointer. > > > > I'm skeptical that will actually work well and be maintainble. E.g. sync_pir_to_ir() > > must be explicitly check for NULL in apic_has_interrupt_for_ppr(), forcing that path > > to do static_call_cond() will be odd. Ditto for ops that are wired up to ioctl()s, > > e.g. the confidential VM stuff, and for ops that are guarded by other stuff, e.g. the > > hypervisor timer. > > > > Actually, it won't just be odd, it will be impossible to disallow NULL a pointer > > for KVM_X86_OP and require static_call_cond() for KVM_X86_OP_NULL. static_call_cond() > > forces the return to "void", so any path that returns a value needs to be manually > > guarded and can't use static_call_cond(), e.g. > > You're right and I should have looked up the series instead of going by > memory. What I did was mostly WARNing on KVM_X86_OP that sets NULL, as > non-NULL ops are the common case. I also added KVM_X86_OP_RET0 to > remove some checks on kvm_x86_ops for ops that return a value. > > All in all I totally agree with patches 2-11 and will apply them (patch > 2 to 5.17 even, as a prerequisite to fix the AVIC race). Several of > patches 13-21 are also mostly useful as it clarifies the code, and the > others I guess are okay in the context of a coherent series though > probably they would have been rejected as one-offs. However, patches 12 > and 22 are unnecessary uses of the C preprocessor in my opinion. > I will send my patches very very soon - I'll rebase on top of this, and review this patch series soon as well. Best regards, Maxim Levitsky > Paolo >
