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

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Message-ID: <c6f47bcf-d75d-4e00-b693-7df97599973c@suse.com>
Date: Sat, 9 Nov 2024 10:29:36 +0100
From: Jürgen Groß <jgross@...e.com>
To: Paolo Bonzini <pbonzini@...hat.com>,
 Sean Christopherson <seanjc@...gle.com>
Cc: 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 09.11.24 09:03, Paolo Bonzini wrote:
> 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?

+1


Juergen

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