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Date:   Thu, 6 Jul 2023 10:45:25 -0700
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Subject: Re: [PATCHv3 0/3] x86/tdx: Fix one more load_unaligned_zeropad()
 issue
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To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>
Cc:     Dexuan Cui <decui@microsoft.com>,
        "rick.p.edgecombe@intel.com" <rick.p.edgecombe@intel.com>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "seanjc@google.com" <seanjc@google.com>,
        "thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20230606095622.1939-1-kirill.shutemov@linux.intel.com>
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From:   Dave Hansen <dave.hansen@intel.com>
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On 7/6/23 09:48, Michael Kelley (LINUX) wrote:
> When a page is transitioning, the caller can and should ensure
> that it is not being accessed during the transition.  But we have
> the load_unaligned_zeropad() wildcard.   So do the following for
> the transition sequence in __set_memory_enc_pgtable():
> 
> 1.  Remove aliasing mappings
> 2.  Remove the PRESENT bit from the PTEs of all transitioning pages
> 3.  Flush the TLB globally
> 4.  Flush the data cache if needed
> 5.  Set/clear the encryption attribute as appropriate
> 6.  Notify the hypervisor of the page status change
> 7.  Add back the PRESENT bit
> 
> With this approach, load_unaligned_zeropad() just takes the
> normal page-fault-based fixup path if it touches a page that is
> transitioning.

Yes, this does seem much simpler.  It funnels everything through the
page fault handler and also doesn't require because careful about the
ordering of the private<=>shared conversions.