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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Dave Hansen" <dave.hansen@intel.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Ingo Molnar" <mingo@kernel.org>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	"Andy Lutomirski" <luto@kernel.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>,
	"Rik van Riel" <riel@surriel.com>,
	"Dave Hansen" <dave.hansen@linux.intel.com>
Subject: Re: [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe()
Date: Tue, 5 Feb 2019 12:17:57 +0100	[thread overview]
Message-ID: <20190205111757.oieqgdcdnctoegav@linutronix.de> (raw)
In-Reply-To: <20190121112117.GA32538@redhat.com>

On 2019-01-21 12:21:17 [+0100], Oleg Nesterov wrote:
> > This is part of our ABI for *sure*.  Inspecting that state is how
> > userspace makes sense of MPX or protection keys faults.  We even use
> > this in selftests/.
> 
> Yes.
> 
> And in any case I do not understand the idea to use the second in-kernel struct fpu.
> A signal handler can be interrupted by another signal, this will need to save/restore
> the FPU state again.

So I assumed that while SIGUSR1 is handled SIGUSR2 will wait until the
current signal is handled. So no interruption. But then SIGSEGV is
probably the exception which will interrupt SIGUSR1. So we would need a
third one…

The idea was to save the FPU state in-kernel so we don't have to
revalidate everything because userspace had access to it and could do
things.
Some things are complicated and not documented why they are the way they
are. For instance on 64bit (based on the code) the signal handler can
remove SSE from the state-mask and the kernel loads the "default-empty"
SSE registers and the enabled states from user. This isn't done on
32bit. Also: we save with XSAVE and allocate the buffer on stack. But if
we can't find the FP_XSTATE_MAGIC* or the buffer is not properly aligned
then we fallback to FXSR and assume that we have a FXSR buffer in front
of us.

> Oleg.

Sebastian

  parent reply	other threads:[~2019-02-05 11:18 UTC|newest]

Thread overview: 91+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09 11:47 [PATCH v6] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 01/22] x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() Sebastian Andrzej Siewior
2019-01-14 16:24   ` Borislav Petkov
2019-02-05 10:08     ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 02/22] x86/fpu: Remove fpu__restore() Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 03/22] x86/fpu: Remove preempt_disable() in fpu__clear() Sebastian Andrzej Siewior
2019-01-14 18:55   ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 04/22] x86/fpu: Always init the `state' " Sebastian Andrzej Siewior
2019-01-14 19:32   ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2019-01-16 19:36   ` Borislav Petkov
2019-01-16 22:40     ` Sebastian Andrzej Siewior
2019-01-17 12:22       ` Borislav Petkov
2019-01-18 21:14         ` Sebastian Andrzej Siewior
2019-01-18 21:17           ` Dave Hansen
2019-01-18 21:37             ` Sebastian Andrzej Siewior
2019-01-18 21:43               ` Dave Hansen
2019-01-21 11:21             ` Oleg Nesterov
2019-01-22 13:40               ` Borislav Petkov
2019-01-22 16:15                 ` Oleg Nesterov
2019-01-22 17:00                   ` Borislav Petkov
2019-02-05 11:34                     ` Sebastian Andrzej Siewior
2019-02-05 11:17               ` Sebastian Andrzej Siewior [this message]
2019-02-26 16:38                 ` Oleg Nesterov
2019-03-08 18:12                   ` Sebastian Andrzej Siewior
2019-02-05 14:37         ` [PATCH 05/22 v2] " Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 06/22] x86/fpu: Don't save fxregs for ia32 frames " Sebastian Andrzej Siewior
2019-01-24 11:17   ` Borislav Petkov
2019-02-05 16:43     ` [PATCH 06/22 v2] x86/fpu: Don't save fxregs for ia32 frames in Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 07/22] x86/fpu: Remove fpu->initialized Sebastian Andrzej Siewior
2019-01-24 13:34   ` Borislav Petkov
2019-02-05 18:03     ` Sebastian Andrzej Siewior
2019-02-06 14:01       ` Borislav Petkov
2019-02-07 10:13         ` Sebastian Andrzej Siewior
2019-02-07 10:37           ` Borislav Petkov
2019-02-05 18:06     ` [PATCH 07/22 v2] " Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 08/22] x86/fpu: Remove user_fpu_begin() Sebastian Andrzej Siewior
2019-01-25 15:18   ` Borislav Petkov
2019-02-05 18:16     ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 09/22] x86/fpu: Add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2019-01-28 18:23   ` Borislav Petkov
2019-02-07 10:43     ` Sebastian Andrzej Siewior
2019-02-13  9:30       ` Borislav Petkov
2019-02-14 14:51         ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 10/22] x86/fpu: Make __raw_xsave_addr() use feature number instead of mask Sebastian Andrzej Siewior
2019-01-28 18:30   ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 11/22] x86/fpu: Make get_xsave_field_ptr() and get_xsave_addr() " Sebastian Andrzej Siewior
2019-01-28 18:49   ` Borislav Petkov
2019-02-07 11:13     ` Sebastian Andrzej Siewior
2019-02-13  9:31       ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 12/22] x86/fpu: Only write PKRU if it is different from current Sebastian Andrzej Siewior
2019-01-23 18:09   ` Dave Hansen
2019-02-07 11:27     ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 13/22] x86/pkeys: Don't check if PKRU is zero before writting it Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 14/22] x86/fpu: Eager switch PKRU state Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 15/22] x86/entry: Add TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2019-01-30 11:55   ` Borislav Petkov
2019-02-07 11:49     ` Sebastian Andrzej Siewior
2019-02-13  9:35       ` Borislav Petkov
2019-02-14 15:28         ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 16/22] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2019-01-30 11:43   ` Borislav Petkov
2019-02-07 13:28     ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 17/22] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2019-01-30 11:56   ` Borislav Petkov
2019-01-30 12:28     ` Sebastian Andrzej Siewior
2019-01-30 12:53       ` Borislav Petkov
2019-02-07 14:10         ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 18/22] x86/fpu: Update xstate's PKRU value on write_pkru() Sebastian Andrzej Siewior
2019-01-23 17:28   ` Dave Hansen
2019-01-09 11:47 ` [PATCH 19/22] x86/fpu: Inline copy_user_to_fpregs_zeroing() Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 20/22] x86/fpu: Let __fpu__restore_sig() restore the !32bit+fxsr frame from kernel memory Sebastian Andrzej Siewior
2019-01-30 21:29   ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 21/22] x86/fpu: Merge the two code paths in __fpu__restore_sig() Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 22/22] x86/fpu: Defer FPU state load until return to userspace Sebastian Andrzej Siewior
2019-01-31  9:16   ` Borislav Petkov
2019-01-15 12:44 ` [PATCH v6] x86: load FPU registers on return to userland David Laight
2019-01-15 13:15   ` 'Sebastian Andrzej Siewior'
2019-01-15 14:33     ` David Laight
2019-01-15 19:46   ` Dave Hansen
2019-01-15 20:26     ` Andy Lutomirski
2019-01-15 20:54       ` Dave Hansen
2019-01-15 21:11         ` Andy Lutomirski
2019-01-16 10:31           ` David Laight
2019-01-16 10:18       ` David Laight
2019-01-30 11:35 ` Borislav Petkov
2019-01-30 12:06   ` Sebastian Andrzej Siewior
2019-01-30 12:27     ` Borislav Petkov
2019-02-08 13:12       ` Sebastian Andrzej Siewior
2019-02-13 15:54         ` Sebastian Andrzej Siewior
2019-02-21 11:49 [PATCH v7] " Sebastian Andrzej Siewior
2019-02-21 11:50 ` [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior

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