From: Thomas Gleixner <tglx@linutronix.de>
To: "Chang S. Bae" <chang.seok.bae@intel.com>,
bp@suse.de, luto@kernel.org, mingo@kernel.org, x86@kernel.org
Cc: len.brown@intel.com, lenb@kernel.org, dave.hansen@intel.com,
thiago.macieira@intel.com, jing2.liu@intel.com,
ravi.v.shankar@intel.com, linux-kernel@vger.kernel.org,
chang.seok.bae@intel.com
Subject: Re: [PATCH v10 13/28] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state
Date: Fri, 01 Oct 2021 22:20:16 +0200 [thread overview]
Message-ID: <87ee944hvj.ffs@tglx> (raw)
In-Reply-To: <871r546b52.ffs@tglx>
Chang,
On Fri, Oct 01 2021 at 17:02, Thomas Gleixner wrote:
> On Wed, Aug 25 2021 at 08:53, Chang S. Bae wrote:
>> +/**
>> + * xfd_switch - Switches the MSR IA32_XFD context if needed.
>> + * @prev: The previous task's struct fpu pointer
>> + * @next: The next task's struct fpu pointer
>> + */
>> +static inline void xfd_switch(struct fpu *prev, struct fpu *next)
>> +{
>> + u64 prev_xfd_mask, next_xfd_mask;
>> +
>> + if (!cpu_feature_enabled(X86_FEATURE_XFD) || !xfeatures_mask_user_dynamic)
>> + return;
>
> This is context switch, so this wants to be a static key which is turned
> on during init when the CPU supports XFD and user dynamic features are
> available.
>
>> +
>> + prev_xfd_mask = prev->state_mask & xfeatures_mask_user_dynamic;
>> + next_xfd_mask = next->state_mask & xfeatures_mask_user_dynamic;
>> +
>> + if (unlikely(prev_xfd_mask != next_xfd_mask))
>> + wrmsrl_safe(MSR_IA32_XFD, xfeatures_mask_user_dynamic ^ next_xfd_mask);
>> +}
>> +
>> /*
>> * Delay loading of the complete FPU state until the return to userland.
>> * PKRU is handled separately.
>> */
>> -static inline void switch_fpu_finish(struct fpu *new_fpu)
>> +static inline void switch_fpu_finish(struct fpu *old_fpu, struct fpu *new_fpu)
>> {
>> - if (cpu_feature_enabled(X86_FEATURE_FPU))
>> + if (cpu_feature_enabled(X86_FEATURE_FPU)) {
>> set_thread_flag(TIF_NEED_FPU_LOAD);
>> + xfd_switch(old_fpu, new_fpu);
>
> Why has this to be done on context switch? Zero explanation provided.
>
> Why can't this be done in exit_to_user() where the FPU state restore is
> handled?
DEFINE_PER_CPU(xfd_state);
update_xfd(fpu)
{
if (__this_cpu_read(xfd_state) != fpu->xfd_state) {
wrmsrl(XFD, fpu->xfd_state);
__this_cpu_write(xfd_state, fpu->xfd_state);
}
}
fpregs_restore_userregs()
{
if (!fpregs_state_valid(fpu, cpu)) {
if (static_branch_unlikely(xfd_switching_enabled))
update_xfd(fpu);
...
}
}
Hmm?
Thanks,
tglx
next prev parent reply other threads:[~2021-10-01 20:20 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-25 15:53 [PATCH v10 00/28] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2021-08-25 15:53 ` [PATCH v10 01/28] x86/fpu/xstate: Fix the state copy function to the XSTATE buffer Chang S. Bae
2021-10-01 12:44 ` Thomas Gleixner
2021-10-03 22:34 ` Bae, Chang Seok
2021-08-25 15:53 ` [PATCH v10 02/28] x86/fpu/xstate: Modify the initialization helper to handle both static and dynamic buffers Chang S. Bae
2021-10-01 12:45 ` Thomas Gleixner
2021-10-03 22:35 ` Bae, Chang Seok
2021-08-25 15:53 ` [PATCH v10 03/28] x86/fpu/xstate: Modify state copy helpers " Chang S. Bae
2021-10-01 12:47 ` Thomas Gleixner
2021-10-03 22:42 ` Bae, Chang Seok
2021-08-25 15:53 ` [PATCH v10 04/28] x86/fpu/xstate: Modify address finders " Chang S. Bae
2021-10-01 13:15 ` Thomas Gleixner
2021-10-03 22:35 ` Bae, Chang Seok
2021-10-04 12:54 ` Thomas Gleixner
2021-08-25 15:53 ` [PATCH v10 05/28] x86/fpu/xstate: Add a new variable to indicate dynamic user states Chang S. Bae
2021-10-01 13:16 ` Thomas Gleixner
2021-10-03 22:35 ` Bae, Chang Seok
2021-10-04 12:57 ` Thomas Gleixner
2021-08-25 15:53 ` [PATCH v10 06/28] x86/fpu/xstate: Add new variables to indicate dynamic XSTATE buffer size Chang S. Bae
2021-10-01 13:32 ` Thomas Gleixner
2021-10-03 22:36 ` Bae, Chang Seok
2021-08-25 15:53 ` [PATCH v10 07/28] x86/fpu/xstate: Calculate and remember dynamic XSTATE buffer sizes Chang S. Bae
2021-08-25 15:53 ` [PATCH v10 08/28] x86/fpu/xstate: Convert the struct fpu 'state' field to a pointer Chang S. Bae
2021-08-25 15:53 ` [PATCH v10 09/28] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically Chang S. Bae
2021-10-01 14:20 ` Thomas Gleixner
2021-10-03 22:36 ` Bae, Chang Seok
2021-08-25 15:53 ` [PATCH v10 10/28] x86/fpu/xstate: Update the XSTATE save function to support dynamic states Chang S. Bae
2021-10-01 15:41 ` Thomas Gleixner
2021-10-02 21:31 ` Thomas Gleixner
2021-10-02 22:54 ` Bae, Chang Seok
2021-10-05 8:16 ` Paolo Bonzini
2021-10-05 7:50 ` Paolo Bonzini
2021-10-05 9:55 ` Thomas Gleixner
2021-08-25 15:53 ` [PATCH v10 11/28] x86/fpu/xstate: Update the XSTATE buffer address finder " Chang S. Bae
2021-08-25 15:53 ` [PATCH v10 12/28] x86/fpu/xstate: Update the XSTATE context copy function " Chang S. Bae
2021-08-25 15:53 ` [PATCH v10 13/28] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state Chang S. Bae
2021-10-01 15:02 ` Thomas Gleixner
2021-10-01 15:10 ` Thomas Gleixner
2021-10-03 22:38 ` Bae, Chang Seok
2021-10-04 12:35 ` Thomas Gleixner
2021-10-01 20:20 ` Thomas Gleixner [this message]
2021-10-03 22:39 ` Bae, Chang Seok
2021-10-04 19:03 ` Thomas Gleixner
2021-10-03 22:41 ` Bae, Chang Seok
2021-08-25 15:53 ` [PATCH v10 14/28] x86/fpu/xstate: Support ptracer-induced XSTATE buffer expansion Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 15/28] x86/arch_prctl: Create ARCH_SET_STATE_ENABLE/ARCH_GET_STATE_ENABLE Chang S. Bae
2021-08-25 16:36 ` Bae, Chang Seok
2021-08-25 15:54 ` [PATCH v10 16/28] x86/fpu/xstate: Support both legacy and expanded signal XSTATE size Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 17/28] x86/fpu/xstate: Adjust the XSAVE feature table to address gaps in state component numbers Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 18/28] x86/fpu/xstate: Disable XSTATE support if an inconsistent state is detected Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 19/28] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 20/28] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 21/28] x86/fpu/amx: Initialize child's AMX state Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 22/28] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 23/28] x86/fpu/xstate: Skip writing zeros to signal frame for dynamic user states if in INIT-state Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 24/28] selftest/x86/amx: Test cases for the AMX state management Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 25/28] x86/insn/amx: Add TILERELEASE instruction to the opcode map Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 26/28] intel_idle/amx: Add SPR support with XTILEDATA capability Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 27/28] x86/fpu/xstate: Add a sanity check for XFD state when saving XSTATE Chang S. Bae
2021-08-25 15:54 ` [PATCH v10 28/28] x86/arch_prctl: ARCH_GET_FEATURES_WITH_KERNEL_ASSISTANCE Chang S. Bae
2021-09-30 21:12 ` [PATCH v10 00/28] x86: Support Intel Advanced Matrix Extensions Len Brown
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