From: Dave Hansen <dave.hansen@intel.com>
To: "Yu, Fenghua" <fenghua.yu@intel.com>,
"H. Peter Anvin" <hpa@linux.intel.com>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
"Mallick, Asit K" <asit.k.mallick@intel.com>,
"Williamson, Glenn P" <glenn.p.williamson@intel.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate_size for xstate size in signal context
Date: Wed, 22 Apr 2015 12:34:02 -0700 [thread overview]
Message-ID: <5537F7AA.3010609@intel.com> (raw)
In-Reply-To: <3E5A0FA7E9CA944F9D5414FEC6C712205C8CE779@ORSMSX106.amr.corp.intel.com>
On 04/22/2015 12:05 PM, Yu, Fenghua wrote:
>> From: Hansen, Dave
>> Sent: Wednesday, April 22, 2015 11:45 AM
>> To: Yu, Fenghua; H. Peter Anvin; Ingo Molnar; Thomas Gleixner; Mallick, Asit
>> K; Williamson, Glenn P
>> Cc: linux-kernel; x86
>> 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.
>
> Xsave->xsave_hdr.xstate_bv is equal to pcntxt_mask (see setup_init_fpu_buf()).
No. I don't think it works this way. xsaves *WRITES* to the
XSTATE_BV[] field in addition to reading it. According to the SDM:
"execution of XSAVES writes the XSTATE_BV field of the XSAVE header (see
Section 13.4.2), setting XSTATE_BV[i] (0 ≤ i ≤ 63) as follows...
Execution of XSAVES performs the init optimization to reduce the amount
of data written to memory. If XINUSE[i] = 0, state component i is not
saved to the XSAVE area (even if RFBM[i] = 1)".
> And here XINUSE and RFBM are irrelevant because they are used in init or modified
> optimization during xsave*/xrstore*. We only copy out the xstates from kernel
> to user and XINUSE and RFBM are not in scope here.
I think they are in use. The kernel created its buffer with 'xsaves' so
when it is reading the buffer it needs to take those optimizations in to
consideration.
next prev parent reply other threads:[~2015-04-22 19:34 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-22 4:51 [PATCH Bugfix v2 0/4] x86/xsave/xsaves: Fix a few xsave/xsaves related bugs Fenghua Yu
2015-04-22 4:51 ` [PATCH Bugfix v2 1/4] x86/xsave.c: Fix xstate offsets and sizes enumeration Fenghua Yu
2015-04-22 4:51 ` [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate_size for xstate size in signal context Fenghua Yu
2015-04-22 18:45 ` Dave Hansen
2015-04-22 19:05 ` Yu, Fenghua
2015-04-22 19:34 ` Dave Hansen [this message]
2015-04-23 0:06 ` Yu, Fenghua
2015-04-23 0:21 ` Dave Hansen
2015-04-23 0:23 ` Yu, Fenghua
2015-04-23 0:34 ` Dave Hansen
2015-04-23 17:09 ` Yu, Fenghua
2015-04-23 21:32 ` Dave Hansen
2015-04-28 14:28 ` Dave Hansen
2015-04-28 22:09 ` Dave Hansen
2015-04-28 22:11 ` Yu, Fenghua
2015-04-29 13:53 ` Dave Hansen
2015-04-22 4:51 ` [PATCH Bugfix v2 3/4] x86/xsaves: Rename xstate_size to kernel_xstate_size to explicitly distinguish xstate size in kernel from user space Fenghua Yu
2015-04-22 4:51 ` [PATCH Bugfix v2 4/4] x86/xsave: Don't add new states in xsave_struct Fenghua Yu
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