linux-kernel - Re: [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate

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Date:	Wed, 22 Apr 2015 11:45:05 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Glenn Williamson <glenn.p.williamson@...el.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate_size
 for xstate size in signal context

On 04/21/2015 09:51 PM, Fenghua Yu wrote:
> +	/*
> +	 * Copy rest of xstates in compact format to user.
> +	 */
> +	for (i = 2; i < xstate_features; i++) {
> +		if (test_bit(i, (unsigned long *)&pcntxt_mask)) {
> +			int user_offset, kernel_offset;
> +			int size;
> +
> +			user_offset = xstate_offsets[i];
> +			kernel_offset = xstate_comp_offsets[i];
> +			size = xstate_sizes[i];
> +
> +			if (__copy_to_user(buf_fx + user_offset,
> +				     xsave + kernel_offset, size))
> +				return -1;
> +		}
> +	}

Is this checking the right bitmap?

The 'xsaves' documentation says: "If RFBM[i] = 1, XSTATE_BV[i] is set to
the value of XINUSE[i]".  Where "XINUSE denotes the state-component
bitmap corresponding to the init optimization".

So shouldn't this be checking xsave->xsave_hdr.xstate_bv instead of
pcntxt_mask?  The will be equal unless the "init optimization" is in play.
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