linux-kernel - RE: [PATCH v7 17/20] x86/virt/tdx: Configure global KeyID on all packages

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Date:   Wed, 30 Nov 2022 20:17:33 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Hansen, Dave" <dave.hansen@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>
CC:     "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: RE: [PATCH v7 17/20] x86/virt/tdx: Configure global KeyID on all
 packages

> On 11/30/22 00:34, Huang, Kai wrote:
> > On Wed, 2022-11-30 at 11:35 +0800, Binbin Wu wrote:
> >> On 11/21/2022 8:26 AM, Kai Huang wrote:
> >>> After the array of TDMRs and the global KeyID are configured to the
> >>> TDX module, use TDH.SYS.KEY.CONFIG to configure the key of the
> >>> global KeyID on all packages.
> >>>
> >>> TDH.SYS.KEY.CONFIG must be done on one (any) cpu for each package.
> >>> And it cannot run concurrently on different CPUs.  Implement a
> >>> helper to run SEAMCALL on one cpu for each package one by one, and
> >>> use it to configure the global KeyID on all packages.
> >>>
> >>> Intel hardware doesn't guarantee cache coherency across different
> >>> KeyIDs.  The kernel needs to flush PAMT's dirty cachelines
> >>> (associated with KeyID 0) before the TDX module uses the global
> >>> KeyID to access the PAMT.  Following the TDX module specification,
> >>> flush cache before configuring the global KeyID on all packages.
> >>>
> >>> Given the PAMT size can be large (~1/256th of system RAM), just use
> >>> WBINVD on all CPUs to flush.
> >>>
> >>> Note if any TDH.SYS.KEY.CONFIG fails, the TDX module may already
> >>> have used the global KeyID to write any PAMT.  Therefore, need to
> >>> use WBINVD to flush cache before freeing the PAMTs back to the
> >>> kernel.  Note using MOVDIR64B (which changes the page's associated
> >>> KeyID from the old TDX private KeyID back to KeyID 0, which is used
> >>> by the kernel)
> >>
> >> It seems not accurate to say MOVDIR64B changes the page's associated
> KeyID.
> >> It just uses the current KeyID for memory operations.
> >
> > The "write" to the memory changes the page's associated KeyID to the
> > KeyID that does the "write".  A more accurate expression perhaps
> > should be MOVDIR64B + MFENSE, but I think it doesn't matter in changelog.
> 
> Just delete it from the changelog.  It's a distraction.  I'm not even sure it's
> *necessary* to do any memory content conversion after the TDX module has
> written gunk.
> 
> There won't be any integrity issues because integrity errors don't do anything for
> KeyID-0 (no #MC).
> 
> I _think_ the reads of the page using KeyID-0 will see abort page semantics.
> That's *FINE*.

I'll remove this from the changelog.  Thanks!