From: Dave Hansen <dave.hansen@intel.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, jannh@google.com,
riel@surriel.com, mingo@redhat.com, bp@suse.de, Jason@zx2c4.com,
luto@kernel.org, tglx@linutronix.de, rkrcmar@redhat.com,
mingo@kernel.org, hpa@zytor.com, kvm@vger.kernel.org,
pbonzini@redhat.com, kurt.kanzenbach@linutronix.de
Subject: Re: [RFC PATCH] x86/fpu: Don't unconditionally add XFEATURE_MASK_FPSSE on sigentry
Date: Fri, 26 Apr 2019 13:44:14 -0700 [thread overview]
Message-ID: <87871e60-4e64-2355-11b4-6201cab8bf75@intel.com> (raw)
In-Reply-To: <20190426200509.3q5ngl44o64q2lg2@linutronix.de>
On 4/26/19 1:05 PM, Sebastian Andrzej Siewior wrote:
>
> copy_fpstate_to_sigframe()
> |
> copy_fpregs_to_sigframe() fails.
> |
> using_compacted_format()
Aw, crud. I was looking at Linus's tree. Sorry about that. In Linus's
tree, if copy_fpregs_to_sigframe() fails, we just return from
copy_fpstate_to_sigframe() immediately. In other words, either XSAVE
works, and we don't have this issue, or XSAVE fails and we don't do the
fixup code in question.
I'll say it again, though: I think we should be using the XSAVE
instruction to save this state. If we need to map some pages in order
to make XSAVE work, then I think we should bring some pages in and we
can do *that* in the slow path. We can even do that without taking page
faults by just calling get_user_pages() for instance.
Or, the slow path could be to fpregs_unlock(), zero the user area
(taking and handling page faults), then fpregs_lock() and retry the
copy_fpregs_to_sigframe().
next prev parent reply other threads:[~2019-04-26 20:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-25 17:35 Sebastian Andrzej Siewior
2019-04-25 21:13 ` Dave Hansen
2019-04-26 7:26 ` Sebastian Andrzej Siewior
2019-04-26 16:33 ` Dave Hansen
2019-04-26 16:50 ` Sebastian Andrzej Siewior
2019-04-26 19:04 ` Dave Hansen
2019-04-26 20:05 ` Sebastian Andrzej Siewior
2019-04-26 20:44 ` Dave Hansen [this message]
2019-04-29 16:39 ` [PATCH] x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails Sebastian Andrzej Siewior
2019-04-29 18:52 ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-30 14:20 ` Dave Hansen
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