Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 3 Aug 2023 14:45:46 +0300
From:   "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>
To:     "Huang, Kai" <kai.huang@intel.com>
Cc:     "Hansen, Dave" <dave.hansen@intel.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "x86@kernel.org" <x86@kernel.org>, "bp@alien8.de" <bp@alien8.de>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "mingo@redhat.com" <mingo@redhat.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>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "n.borisov.lkml@gmail.com" <n.borisov.lkml@gmail.com>
Subject: Re: [PATCH v3 07/12] x86/tdx: Make TDX_HYPERCALL asm similar to
 TDX_MODULE_CALL
Message-ID: <20230803114546.em5qsjs33i5b7ogh@box.shutemov.name>
References: <cover.1690369495.git.kai.huang@intel.com>
 <6f92d08855491b3e9ff1221d2bb7af873d546afd.1690369495.git.kai.huang@intel.com>
 <20230727171008.aw3z6oxh4vfnahep@box.shutemov.name>
 <e75603996f88941892a19181c852ecfdc9adf06c.camel@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <e75603996f88941892a19181c852ecfdc9adf06c.camel@intel.com>
Precedence: bulk

On Thu, Jul 27, 2023 at 11:05:35PM +0000, Huang, Kai wrote:
> On Thu, 2023-07-27 at 20:10 +0300, kirill.shutemov@linux.intel.com wrote:
> > On Wed, Jul 26, 2023 at 11:25:09PM +1200, Kai Huang wrote:
> > > 
> > > Remove the __tdx_hypercall_ret() as __tdx_hypercall() already does so.
> > 
> > Hm. So we now update struct on all VMCALLs. Is it a good idea??
> > 
> 
> Do you mean we "unconditionally save output registers to  the structure", right?
> 
> > We give
> > more control to VMM where it is not needed.?
> > 
> 
> I don't quite follow this.  Can you elaborate?
> 
> Do you worry about VMM being malicious and putting malicious values to the
> registers?

Yes. Caller of the hypercall may expect that the register is in-only and
re-use the field for other stuff. And it would work until VMM decide
otherwise.

> > I would rather keep the struct
> > read-only where possible.
> > 
> 
> We can achieve this if there's a clean way to do, but I don't see that.

Keep _ret() and non-_ret() versions?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov