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From: "Liu, Jing2" <jing2.liu@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	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>,
	"Cooper, Andrew" <andrew.cooper3@citrix.com>
Subject: RE: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core
Date: Fri, 15 Oct 2021 09:00:33 +0000	[thread overview]
Message-ID: <BYAPR11MB3256D90BEEDE57988CA39705A9B99@BYAPR11MB3256.namprd11.prod.outlook.com> (raw)
In-Reply-To: <3997787e-402d-4b2b-0f90-4a672c77703f@redhat.com>


On 10/14/2021 11:01 PM, Paolo Bonzini wrote:
[...]
> Calls into the function, but doesn't necessarily allocate anything.
> What you wrote below looks correct to me, thanks.
> 

For the guest dynamic state support, based on the latest discussion,
four copies of XFD need be cared and switched, I'd like to list as follows.

- vcpu->arch.xfd: this is the real guest value for running.
Since kernel init XFD before XCR0, so I think KVM can initialize it as
bit[n]=0, for a guest start value. Otherwise, kvm_arch_vcpu_create()
need initializes vcpu->arch.xfd=guest_fpu->xfd=user_fpu->xfd=1.
Guest wrmsr XFD trap will make it update.

- user_fpu->fpstate->xfd: Qemu itself and not for guest, which is
probably always set.

- guest_fpu->fpstate->xfd: this is for KVM internal value between time[*].
KVM reinitializes it as bit[n]=0 (not the same as user_fpu), and it will be
updated when guest wrmsr trap. Thus, before passthrough, it's the same
as vcpu->arch.xfd, thus vmenter/vmexit need not rewrite msr.
After passthrough, this keeps bit[n] as 0 forever.

- current_fpu->fpstate->xfd: it should be the same as KVM internal value
between time[*].
[*] this means between kvm_load_guest_fpu and kvm_put_guest_fpu.

From guest booting timeline,  the values are: 

Booting start...   # In this time, vcpu->arch.xfd[n]=guest_fpu->xfd[n]=0
Init XFD by WRMSR(XFD[n], 1)  	# Then, vcpu->arch.xfd[n]=guest_fpu->xfd[n]=1
Init XCR0 by XSETBV 	
...
#NM WRMSR(XFD[n], 0)  # Then, guest_fpu->xfd[n]=0, vcpu->arch.xfd[n]=0.
vcpu->arch.xfd will be updated in later vmexits. 

BTW, we only need lazy-passthrough XFD WRITE and passthrough
READ directly.

Thanks,
Jing

> Paolo
> 
> > Also you really should not wait until _all_ dynamic states are cleared
> > in guest XFD.  Because a guest which has bit 18 and 19 available but
> > only > uses one of them is going to trap on every other context switch due
> to XFD writes.


  parent reply	other threads:[~2021-10-15  9:00 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 [this message]
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
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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