linux-kernel - Re: [PATCH v4 10/10] x86/xsaves: Re-enable XSAVES

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Message-ID: <572A7BD5.7040708@intel.com>
Date:	Wed, 4 May 2016 15:46:45 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Dave Hansen <dave.hansen@...ux.intel.com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:	Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v4 10/10] x86/xsaves: Re-enable XSAVES

On 05/04/2016 03:41 PM, Dave Hansen wrote:
> But, since we *always* call XSAVES with an instruction mask of -1 and
> end up with a requested feature bitmap (RFBM) equal to XCR0, I think we
> can do a shortcut because we'll practically *always* have an
> xcomp_bv==RFBM==XCR0, which means that all (present) components will
> always have an address.

Actually, we depend on that anyway.  xstate_comp_offsets[] is completely
bogus if we don't have xcomp_bv==RFBM==XCR0.

Perhaps we need to add those checks anyway.