linux-kernel - Re: [PATCH 07/10] x86/tdx: Extend TDX_MODULE_CALL to support more TDCALL/SEAMCALL leafs

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Message-ID: <a2218af09553f89674d3ba3d59db31d2521745e3.camel@intel.com>
Date:   Thu, 13 Jul 2023 10:24:48 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH 07/10] x86/tdx: Extend TDX_MODULE_CALL to support more
 TDCALL/SEAMCALL leafs

On Thu, 2023-07-13 at 10:19 +0000, Huang, Kai wrote:
> On Thu, 2023-07-13 at 10:43 +0200, Peter Zijlstra wrote:
> > On Thu, Jul 13, 2023 at 08:02:54AM +0000, Huang, Kai wrote:
> > 
> > > Sorry I am ignorant here.  Won't "clearing ECX only" leave high bits of
> > > registers still containing guest's value?
> > 
> > architecture zero-extends 32bit stores
> 
> Sorry, where can I find this information? Looking at SDM I couldn't find :-(
> 
> 

Hmm.. I think I found it -- it's in SDM vol 1:

3.4.1.1 General-Purpose Registers in 64-Bit Mode

32-bit operands generate a 32-bit result, zero-extended to a 64-bit result in
the destination general-purpose register.

Sorry for the noise!