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Date:   Tue, 6 Jun 2023 21:37:18 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        decui@microsoft.com, rick.p.edgecombe@intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com, seanjc@google.com,
        thomas.lendacky@amd.com, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCHv3 2/3] x86/tdx: Fix race between set_memory_encrypted()
 and load_unaligned_zeropad()
Message-ID: <20230606183718.i3iqwbk7gdomiq5s@box.shutemov.name>
References: <20230606095622.1939-1-kirill.shutemov@linux.intel.com>
 <20230606095622.1939-3-kirill.shutemov@linux.intel.com>
 <f7f82377-6127-79e3-07d8-def490c4e35c@intel.com>
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On Tue, Jun 06, 2023 at 11:14:29AM -0700, Dave Hansen wrote:
> On 6/6/23 02:56, Kirill A. Shutemov wrote:
> > load_unaligned_zeropad() can touch memory that is not owned by the
> > caller, but just happened to next after the owned memory.
> > This load_unaligned_zeropad() behaviour makes it important when kernel
> > asks VMM to convert a GPA from shared to private or back. Kernel must
> > never have a page mapped into direct mapping (and aliases) as private
> > when the GPA is already converted to shared or when GPA is not yet
> > converted to private.
> > 
> > load_unaligned_zeropad() can touch memory that is not owned by the
> > caller, but just happens to be next after the owned memory. This
> > load_unaligned_zeropad() behavior makes it important when the kernel
> > asks VMM to convert a GPA from shared to private or back. The kernel
> > must never have a page mapped into direct mapping (and aliases) as
> > private when the GPA is already converted to shared or when the GPA is
> > not yet converted to private.
> 
> Heh, that must be really important info to have it in the changelog twice!
> 
> I'll fix it up when I apply it.

Ouch. Please fix the comment in the code too.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov