From: Thomas Gleixner <tglx@linutronix.de>
To: Paolo Bonzini <pbonzini@redhat.com>,
"Liu, Jing2" <jing2.liu@intel.com>,
LKML <linux-kernel@vger.kernel.org>
Cc: "x86@kernel.org" <x86@kernel.org>,
"Bae, Chang Seok" <chang.seok.bae@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Arjan van de Ven <arjan@linux.intel.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"Nakajima, Jun" <jun.nakajima@intel.com>,
Jing Liu <jing2.liu@linux.intel.com>,
"seanjc@google.com" <seanjc@google.com>,
Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core
Date: Thu, 14 Oct 2021 16:23:34 +0200 [thread overview]
Message-ID: <87tuhj65y1.ffs@tglx> (raw)
In-Reply-To: <0a5aa9d3-e0d4-266e-5e25-021a5ea9c611@redhat.com>
On Thu, Oct 14 2021 at 14:26, Paolo Bonzini wrote:
> On 14/10/21 14:23, Thomas Gleixner wrote:
>>> In principle I don't like it very much; it would be nicer to say "you
>>> enable it for QEMU itself via arch_prctl(ARCH_SET_STATE_ENABLE), and for
>>> the guests via ioctl(KVM_SET_CPUID2)". But I can see why you want to
>>> keep things simple, so it's not a strong objection at all.
>> Errm.
>>
>> qemu()
>> read_config()
>> if (dynamic_features_passthrough())
>> request_permission(feature) <- prctl(ARCH_SET_STATE_ENABLE)
>>
>> create_vcpu_threads()
>> ....
>>
>> vcpu_thread()
>> kvm_ioctl(ENABLE_DYN_FEATURE, feature) <- KVM ioctl
>>
>> That's what I lined out, right?
>>
>
> I meant prctl for QEMU-in-user-mode vs. ioctl QEMU-in-guest-mode (i.e.
> no prctl if only the guest uses it). But anyway it's just abstract
> "beauty", let's stick to simple. :)
It's not about simple. It's about correctness in the first place.
The prctl() is process wide and grants permission. If that permission is
not granted, e.g. by a seccomp rule, then the vCPU threads cannot use it
either. We are _not_ making exceptions for KVM just because it's KVM.
Trying to pretend that the usermode thread does not need it is just
illusion. The kernel representation of that very usermode vCPU thread must
have a large fpstate. It still can have XFD set, but that's a detail.
So what you are trying to sell me has nothing to do with beauty at all
except when your definition of beauty originates from a tunnel of horrors.
Thanks,
tglx
next prev parent reply other threads:[~2021-10-14 14:23 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-11 23:59 [patch 00/31] x86/fpu: Preparatory cleanups for AMX support (part 1) Thomas Gleixner
2021-10-11 23:59 ` [patch 01/31] x86/fpu: Remove pointless argument from switch_fpu_finish() Thomas Gleixner
2021-10-12 0:00 ` [patch 02/31] x86/fpu: Update stale comments Thomas Gleixner
2021-10-12 0:00 ` [patch 03/31] x86/pkru: Remove useless include Thomas Gleixner
2021-10-12 0:00 ` [patch 04/31] x86/fpu: Restrict xsaves()/xrstors() to independent states Thomas Gleixner
2021-10-12 14:24 ` Borislav Petkov
2021-10-12 0:00 ` [patch 05/31] x86/fpu: Cleanup the on_boot_cpu clutter Thomas Gleixner
2021-10-12 0:00 ` [patch 06/31] x86/fpu: Remove pointless memset in fpu_clone() Thomas Gleixner
2021-10-12 0:00 ` [patch 07/31] x86/process: Clone FPU in copy_thread() Thomas Gleixner
2021-10-12 0:00 ` [patch 08/31] x86/fpu: Do not inherit FPU context for kernel and IO worker threads Thomas Gleixner
2021-10-12 0:00 ` [patch 09/31] x86/fpu: Do not inherit FPU context for CLONE_THREAD Thomas Gleixner
2021-10-12 16:10 ` Borislav Petkov
2021-10-12 18:52 ` Thomas Gleixner
2021-10-12 19:01 ` Thomas Gleixner
2021-10-12 0:00 ` [patch 10/31] x86/fpu: Cleanup xstate xcomp_bv initialization Thomas Gleixner
2021-10-12 0:00 ` [patch 11/31] x86/fpu/xstate: Provide and use for_each_xfeature() Thomas Gleixner
2021-10-12 16:45 ` Borislav Petkov
2021-10-12 0:00 ` [patch 12/31] x86/fpu/xstate: Mark all init only functions __init Thomas Gleixner
2021-10-12 0:00 ` [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core Thomas Gleixner
2021-10-12 16:53 ` Borislav Petkov
2021-10-12 18:25 ` Thomas Gleixner
2021-10-12 18:26 ` Thomas Gleixner
2021-10-12 17:22 ` Paolo Bonzini
2021-10-13 6:15 ` Liu, Jing2
2021-10-13 6:26 ` Paolo Bonzini
2021-10-13 7:46 ` Liu, Jing2
2021-10-13 8:42 ` Paolo Bonzini
2021-10-13 10:14 ` Andy Lutomirski
2021-10-13 12:26 ` Paolo Bonzini
2021-10-13 14:14 ` Thomas Gleixner
2021-10-13 14:24 ` Thomas Gleixner
2021-10-13 14:59 ` Andy Lutomirski
2021-10-13 15:05 ` Paolo Bonzini
2021-10-13 10:25 ` Liu, Jing2
2021-10-13 12:37 ` Paolo Bonzini
2021-10-13 14:06 ` Thomas Gleixner
2021-10-14 6:50 ` Paolo Bonzini
2021-10-14 8:02 ` Liu, Jing2
2021-10-14 9:01 ` Paolo Bonzini
2021-10-14 11:21 ` Liu, Jing2
2021-10-14 11:33 ` Paolo Bonzini
2021-10-14 11:30 ` Liu, Jing2
2021-10-14 11:39 ` Paolo Bonzini
2021-11-22 8:50 ` Liu, Jing2
2021-10-14 14:09 ` Thomas Gleixner
2021-10-14 14:37 ` Thomas Gleixner
2021-10-14 15:01 ` Paolo Bonzini
2021-10-14 19:14 ` Thomas Gleixner
2021-10-15 9:20 ` Liu, Jing2
2021-10-15 9:36 ` Thomas Gleixner
2021-10-15 14:24 ` Liu, Jing2
2021-10-15 15:53 ` Paolo Bonzini
2021-10-16 14:45 ` Thomas Gleixner
2021-10-15 9:00 ` Liu, Jing2
2021-10-15 10:50 ` Thomas Gleixner
2021-10-15 11:17 ` Paolo Bonzini
2021-10-15 13:01 ` Liu, Jing2
2021-10-14 12:23 ` Thomas Gleixner
2021-10-14 12:26 ` Paolo Bonzini
2021-10-14 14:23 ` Thomas Gleixner [this message]
2021-10-13 15:12 ` Thomas Gleixner
2021-10-14 8:21 ` Liu, Jing2
2021-10-14 13:08 ` Thomas Gleixner
2021-10-12 0:00 ` [patch 14/31] x86/fpu: Replace KVMs homebrewn FPU copy from user Thomas Gleixner
2021-10-12 17:00 ` Borislav Petkov
2021-10-13 14:57 ` Sean Christopherson
2021-10-13 15:12 ` Paolo Bonzini
2021-10-13 15:16 ` Thomas Gleixner
2021-10-12 17:30 ` Paolo Bonzini
2021-10-12 0:00 ` [patch 15/31] x86/fpu: Rework copy_xstate_to_uabi_buf() Thomas Gleixner
2021-10-12 17:30 ` Paolo Bonzini
2021-10-12 0:00 ` [patch 16/31] x86/fpu: Replace KVMs homebrewn FPU copy to user Thomas Gleixner
2021-10-12 17:10 ` Borislav Petkov
2021-10-12 17:36 ` Paolo Bonzini
2021-10-12 17:47 ` Thomas Gleixner
2021-10-12 18:40 ` [patch V2 16/31] x86/fpu: Replace KVMs home brewed " Thomas Gleixner
2021-10-13 5:34 ` [patch 16/31] x86/fpu: Replace KVMs homebrewn " Paolo Bonzini
2021-10-12 0:00 ` [patch 17/31] x86/fpu: Mark fpu__init_prepare_fx_sw_frame() as __init Thomas Gleixner
2021-10-12 0:00 ` [patch 18/31] x86/fpu: Move context switch and exit to user inlines into sched.h Thomas Gleixner
2021-10-12 0:00 ` [patch 19/31] x86/fpu: Clean up cpu feature tests Thomas Gleixner
2021-10-12 0:00 ` [patch 20/31] x86/fpu: Make os_xrstor_booting() private Thomas Gleixner
2021-10-12 0:00 ` [patch 21/31] x86/fpu: Move os_xsave() and os_xrstor() to core Thomas Gleixner
2021-10-12 0:00 ` [patch 22/31] x86/fpu: Move legacy ASM wrappers " Thomas Gleixner
2021-10-12 0:00 ` [patch 23/31] x86/fpu: Make WARN_ON_FPU() private Thomas Gleixner
2021-10-12 0:00 ` [patch 24/31] x86/fpu: Move fpregs_restore_userregs() to core Thomas Gleixner
2021-10-12 17:32 ` Borislav Petkov
2021-10-12 0:00 ` [patch 25/31] x86/fpu: Move mxcsr related code " Thomas Gleixner
2021-10-12 0:00 ` [patch 26/31] x86/fpu: Move fpstate functions to api.h Thomas Gleixner
2021-10-12 17:46 ` Borislav Petkov
2021-10-12 0:00 ` [patch 27/31] x86/fpu: Remove internal.h dependency from fpu/signal.h Thomas Gleixner
2021-10-12 0:00 ` [patch 28/31] x86/sev: Include fpu/xcr.h Thomas Gleixner
2021-10-12 7:24 ` Xiaoyao Li
2021-10-12 0:00 ` [patch 29/31] x86/fpu: Mop up the internal.h leftovers Thomas Gleixner
2021-10-12 0:00 ` [patch 30/31] x86/fpu: Replace the includes of fpu/internal.h Thomas Gleixner
2021-10-12 0:00 ` [patch 31/31] x86/fpu: Provide a proper function for ex_handler_fprestore() Thomas Gleixner
2021-10-12 21:15 ` [patch 00/31] x86/fpu: Preparatory cleanups for AMX support (part 1) Thomas Gleixner
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