linux-kernel - Re: [PATCH] KVM/x86: don't use a literal 1 instead of RET_PF

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Message-ID: <54f44f6a-f504-4b56-a70f-cf96720ff1b8@redhat.com>
Date: Sat, 9 Nov 2024 09:03:36 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
 x86@...nel.org, kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "H . Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] KVM/x86: don't use a literal 1 instead of RET_PF_RETRY

On 11/8/24 19:44, Sean Christopherson wrote:
> On Fri, Nov 08, 2024, Paolo Bonzini wrote:
>> Queued, thanks.
> 
> Noooo!  Can you un-queue?

Yes, I hadn't even pushed it to kvm/queue.  I applied it out of a whim 
but then realized that it wasn't really -rc7 material.

> The return from kvm_mmu_page_fault() is NOT RET_PF_xxx, it's KVM outer 0/1/-errno.
> I.e. '1' is saying "resume the guest", it has *nothing* to do with RET_PF_RETRY.
> E.g. that path also handles RET_PF_FIXED, RET_PF_SPURIOUS, etc.

Gah, I even checked the function and was messed up by the other "return 
RET_PF_RETRY".

If you add X86EMUL_* to the mix, it's even worse.  I had to read this 
three times to understand that it was *not* returning X86EMUL_CONTINUE 
by mistake.  Can I haz strongly-typed enums like in C++?...

         r = kvm_check_emulate_insn(vcpu, emulation_type, insn, insn_len);
         if (r != X86EMUL_CONTINUE) {
		...
         }

         if (!(emulation_type & EMULTYPE_NO_DECODE)) {
                 kvm_clear_exception_queue(vcpu);
                 if (kvm_vcpu_check_code_breakpoint(vcpu, 
emulation_type, &r))
                         return r;
		...
	}

So yeah this really has to be fixed the right way, after all even 
RET_PF_* started out as a conversion from 0/1.

Obligatory bikeshedding, how do KVM_RET_USER and KVM_RET_GUEST sound like?

Paolo