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Date: Tue, 31 Jan 2023 10:39:48 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bp@alien8.de>,
	Andy Lutomirski <luto@kernel.org>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Elena Reshetova <elena.reshetova@intel.com>, x86@kernel.org,
	linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
	kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] x86/tdx: Do not corrupt frame-pointer in
 __tdx_hypercall()
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References: <20230130135354.27674-1-kirill.shutemov@linux.intel.com>
 <Y9jShNfS/d8LGu8w@hirez.programming.kicks-ass.net>
 <20230131083901.ssg5huno2lhrbmzg@box.shutemov.name>
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In-Reply-To: <20230131083901.ssg5huno2lhrbmzg@box.shutemov.name>

On Tue, Jan 31, 2023 at 11:39:01AM +0300, Kirill A. Shutemov wrote:
> On Tue, Jan 31, 2023 at 09:34:12AM +0100, Peter Zijlstra wrote:
> > On Mon, Jan 30, 2023 at 04:53:54PM +0300, Kirill A. Shutemov wrote:
> > > If compiled with CONFIG_FRAME_POINTER=y, objtool in not happy that
> > > __tdx_hypercall() messes up RBP.
> > > 
> > >   objtool: __tdx_hypercall+0x7f: return with modified stack frame
> > > 
> > > Rework the function to store TDX_HCALL_ flags on stack instead of RBP.
> > 
> > Also, on IRC you mentioned that per TDX spec, BP is a valid argument
> > register too and you were going to raise this and get it fixed, TDX
> > hypercalls must not use BP to pass data.
> 
> I've raised the question yesterday. No progress so far. It will take time
> to get it into the public spec.

Sure, just making sure it's not forgotten about. Thanks!