linux-kernel - Re: [RFC PATCH v2 3/6] KVM: x86/mmu: Pass round full 64-bit error code for the KVM page fault

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Message-ID: <37b868c53c9f35e8ec051573562a4598df38d72d.camel@intel.com>
Date:   Thu, 22 Jun 2023 23:28:22 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC:     "michael.roth@....com" <michael.roth@....com>,
        "Annapurve, Vishal" <vannapurve@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "ackerleytng@...gle.com" <ackerleytng@...gle.com>,
        "Chen, Bo2" <chen.bo@...el.com>, "Shahar, Sagi" <sagis@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "zhi.wang.linux@...il.com" <zhi.wang.linux@...il.com>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>
Subject: Re: [RFC PATCH v2 3/6] KVM: x86/mmu: Pass round full 64-bit error
 code for the KVM page fault

On Thu, 2023-06-22 at 16:16 -0700, Yamahata, Isaku wrote:
> The upper 32 bits of error code are discarded at kvm_mmu_page_fault()
> by lower_32_bits().  Now it's passed down as full 64 bits.
> Because only FNAME(page_fault) depends on it, move lower_32_bits() into
> FNAME(page_fault).

I haven't looked into the code yet, but the last sentence around
FNAME(page_fault) doesn't make a lot sense IIUC?

For instance, we can have a shadow EPT table when EPT is enabled in L0 and
exposed to L1.  If we want to pass 64-bit error code to the handler, how can
FRAME(page_fault)() depend on the lower 32-bit value?