linux-kernel - Re: [PATCH] KVM: x86/mmu: Guard against collision with KVM-defined PFERR_IMPLICIT

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Message-ID: <caf35fecfa517794385006616d580544a6dd7866.camel@intel.com>
Date:   Mon, 31 Jul 2023 09:35:36 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86/mmu: Guard against collision with KVM-defined
 PFERR_IMPLICIT_ACCESS

On Fri, 2023-07-21 at 15:37 -0700, Sean Christopherson wrote:
> Add an assertion in kvm_mmu_page_fault() to ensure the error code provided
> by hardware doesn't conflict with KVM's software-defined IMPLICIT_ACCESS
> flag.  In the unlikely scenario that future hardware starts using bit 48
> for a hardware-defined flag, preserving the bit could result in KVM
> incorrectly interpreting the unknown flag as KVM's IMPLICIT_ACCESS flag.
> 
> WARN so that any such conflict can be surfaced to KVM developers and
> resolved, but otherwise ignore the bit as KVM can't possibly rely on a
> flag it knows nothing about.
> 
> Fixes: 4f4aa80e3b88 ("KVM: X86: Handle implicit supervisor access with SMAP")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Acked-by: Kai Huang <kai.huang@...el.com>