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Date: Tue, 05 May 2015 13:12:54 -0700
From: Dave Hansen <dave.hansen@linux.intel.com>
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To: Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org
CC: Andy Lutomirski <luto@amacapital.net>, Borislav Petkov <bp@alien8.de>,
        Fenghua Yu <fenghua.yu@intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 201/208] x86/fpu: Clean up xstate feature reservation
References: <1430848712-28064-1-git-send-email-mingo@kernel.org> <1430848712-28064-41-git-send-email-mingo@kernel.org>
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On 05/05/2015 10:58 AM, Ingo Molnar wrote:
>  struct xregs_state {
>  	struct fxregs_state		i387;
>  	struct xstate_header		header;
> -	struct ymmh_struct		ymmh;
> -	struct lwp_struct		lwp;
> -	struct bndreg			bndreg[4];
> -	struct bndcsr			bndcsr;
> -	/* New processor state extensions will go here. */
> +	u8				__reserved[XSTATE_RESERVE];
>  } __attribute__ ((packed, aligned (64)));

Just to reiterate.  The size of 'XSTATE_RESERVE' is completely unknown
at compile time.  It's wrong in the existing kernel, but we should fix
it up instead of mucking with it like this.