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Date:   Thu, 13 Jul 2023 12:39:46 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Huang, Kai" <kai.huang@intel.com>
Cc:     "Hansen, Dave" <dave.hansen@intel.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "bp@alien8.de" <bp@alien8.de>, "x86@kernel.org" <x86@kernel.org>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Yamahata, Isaku" <isaku.yamahata@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Subject: Re: [PATCH 07/10] x86/tdx: Extend TDX_MODULE_CALL to support more
 TDCALL/SEAMCALL leafs
Message-ID: <20230713103946.GG3139243@hirez.programming.kicks-ass.net>
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On Thu, Jul 13, 2023 at 10:24:48AM +0000, Huang, Kai wrote:
> 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.

Yes, that's it.