linux-kernel - Re: [PATCH v9 4/6] KVM: x86: Introduce untag_addr() in kvm_x86

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Message-ID: <bf98965c-51c5-aaaa-efd9-ce2ecf1c2cbb@linux.intel.com>
Date:   Fri, 30 Jun 2023 01:26:31 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, chao.gao@...el.com, kai.huang@...el.com,
        David.Laight@...lab.com, robert.hu@...ux.intel.com
Subject: Re: [PATCH v9 4/6] KVM: x86: Introduce untag_addr() in kvm_x86_ops



On 6/29/2023 11:16 PM, Sean Christopherson wrote:
>> And for LAM, X86EMUL_F_IMPLICIT will not be used because in the implicit
>> access to memory management registers or descriptors,
>> the linear base addresses still need to be canonical and no hooks will be
>> added to untag the addresses in these pathes.
>> So I probably will remove the check for X86EMUL_F_IMPLICIT here.
> No, please keep it, e.g. so that changes in the emulator don't lead to breakage,
> and to document that they are exempt.
>
> If you want, you could do WARN_ON_ONCE() for the IMPLICIT case, but I don't know
> that that's worthwhile, e.g. nothing will go wrong if KVM tries to untag an
> implicit access, and deliberately avoiding the call make make it annoying to
> consolidate code in the future.
Right.
Have a second thought, X86EMUL_F_IMPLICIT should be kept in case SVM has 
a different implementation and needs to do untag for IMPLICIT cases.