From: Andy Lutomirski <luto@amacapital.net>
To: Rik van Riel <riel@surriel.com>
Cc: "Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
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>
Subject: Re: [RFC PATCH 04/10] x86/fpu: eager switch PKRU state
Date: Wed, 12 Sep 2018 08:49:01 -0700 [thread overview]
Message-ID: <7C1494C8-C6CA-4599-A6B3-0833F358E3A2@amacapital.net> (raw)
In-Reply-To: <a1ee2e5226c780312bd8ef5658f4b6422e7cf434.camel@surriel.com>
> On Sep 12, 2018, at 8:30 AM, Rik van Riel <riel@surriel.com> wrote:
>
> On Wed, 2018-09-12 at 08:20 -0700, Andy Lutomirski wrote:
>>>
>>> --- a/arch/x86/mm/pkeys.c
>>> +++ b/arch/x86/mm/pkeys.c
>>> @@ -18,6 +18,20 @@
>>>
>>> #include <asm/cpufeature.h> /* boot_cpu_has,
>>> ... */
>>> #include <asm/mmu_context.h> /*
>>> vma_pkey() */
>>> +#include <asm/fpu/internal.h>
>>> +
>>> +void write_pkru(u32 pkru)
>>> +{
>>> + if (!boot_cpu_has(X86_FEATURE_OSPKE))
>>> + return;
>>> +
>>> + current->thread.fpu.pkru = pkru;
>>> +
>>
>> I thought that the offset of PKRU in the xstate was fixed after boot.
>
> You are right, it is. However, that offset would need
> to be stored somewhere, and the value read every time
> we wanted to read or store the PKRU value from/to the
> floating point state.
>
> I suspect that would not be any faster than keeping a
> copy of the PKRU value in a known location.
>
>> Anyway, as written, this needs a lockdep assertion that we’re not
>> preemptible, an explicit preempt_disable(), or a comment explaining
>> why it’s okay if we get preempted in this function.
>>
>>> + __fpregs_changes_begin();
>
> This handles the preemption disabling, see patch
> 3 of the series.
Sure, but the first write is *before* this. So we can be preempted with the two copies of PKRU being out of sync.
>
>>> + __fpregs_load_activate(¤t->thread.fpu,
>>> smp_processor_id());
>>> + __write_pkru(pkru);
>>> + __fpregs_changes_end();
>>> +}
>>>
>>> int __execute_only_pkey(struct mm_struct *mm)
>>> {
>>> --
>>> 2.19.0
>>>
>>
>>
> --
> All Rights Reversed.
next prev parent reply other threads:[~2018-09-12 15:49 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-12 13:33 [RFC PATCH] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 01/10] x86/entry: remove _TIF_ALLWORK_MASK Sebastian Andrzej Siewior
2018-09-27 14:21 ` Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 02/10] kvm: x86: make kvm_{load|put}_guest_fpu() static Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 03/10] x86/fpu: add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 04/10] x86/fpu: eager switch PKRU state Sebastian Andrzej Siewior
2018-09-12 14:18 ` Paolo Bonzini
2018-09-12 15:24 ` Andy Lutomirski
2018-09-12 15:30 ` Paolo Bonzini
2018-09-14 20:35 ` [RFC PATCH 04/10 v2 ] " Sebastian Andrzej Siewior
2018-09-17 8:37 ` Paolo Bonzini
2018-09-18 14:27 ` Sebastian Andrzej Siewior
2018-09-18 15:07 ` Paolo Bonzini
2018-09-18 15:11 ` Rik van Riel
2018-09-18 15:29 ` Paolo Bonzini
2018-09-18 16:04 ` Sebastian Andrzej Siewior
2018-09-18 17:29 ` Rik van Riel
2018-09-19 5:55 ` Paolo Bonzini
2018-09-19 16:57 ` Sebastian Andrzej Siewior
2018-09-19 17:00 ` Paolo Bonzini
2018-09-19 17:19 ` Sebastian Andrzej Siewior
2018-09-19 19:38 ` Rik van Riel
2018-09-19 19:49 ` Andy Lutomirski
2018-09-12 15:20 ` [RFC PATCH 04/10] " Andy Lutomirski
2018-09-12 15:30 ` Rik van Riel
2018-09-12 15:49 ` Andy Lutomirski [this message]
2018-09-19 16:58 ` Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 05/10] x86/pkeys: Drop the preempt-disable section Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 06/10] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 07/10] x86/entry: add TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 08/10] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 09/10] x86/fpu: copy non-resident FPU state at fork time Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 10/10] x86/fpu: defer FPU state load until return to userspace Sebastian Andrzej Siewior
2018-09-12 15:47 ` Andy Lutomirski
2018-09-19 17:05 ` Sebastian Andrzej Siewior
2018-09-21 3:45 ` Andy Lutomirski
2018-09-21 4:15 ` Andy Lutomirski
2018-09-26 11:12 ` Sebastian Andrzej Siewior
2018-09-26 14:34 ` Andy Lutomirski
2018-09-26 15:32 ` Sebastian Andrzej Siewior
2018-09-26 16:24 ` Andy Lutomirski
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