Re: [RFC PATCH 1/1] x86/sgx: Explicitly give up the CPU in EDMM's ioctl() to avoid softlockup

[Jarkko Sakkinen]

On Tue Apr 23, 2024 at 2:50 PM EEST, Huang, Kai wrote:
> On Tue, 2024-04-23 at 17:25 +0800, 朱伯君(杰铭) wrote:
> > EDMM's ioctl()s support batch operations, which may be
> > time-consuming. Try to explicitly give up the CPU at
> > the every end of "for loop" in
> > sgx_enclave_{ modify_types | restrict_permissions | remove_pages}
> > to give other tasks a chance to run, and avoid softlockup warning.
> > 
> > The following has been observed on Linux v6.9-rc5 with kernel
> > preemptions disabled(by configuring "PREEMPT_NONE=y"), when kernel
> > is requested to restrict page permissions of a large number of EPC pages.
> > 
> >     ------------[ cut here ]------------
> >     watchdog: BUG: soft lockup - CPU#45 stuck for 22s! [occlum-run:3905]
> >     ...
> >     CPU: 45 PID: 3905 Comm: occlum-run Not tainted 6.9.0-rc5 #7
> >     ...
> >     RIP: 0010:sgx_enclave_restrict_permissions+0xba/0x1f0
> >     Code: 48 c1 e6 05 48 89 d1 48 8d 5c 24 40 b8 0e 00 00 00 48 2b 8e 70 8e f5 93 48 c1 e9 05 48 c1 e1 0c 48 03 8e 68 8e f5 93 0f 01 cf <a9> 00 00 00 40 0f 85 b2 00 00 00 85 c0 0f 85 db 00 00 00 4c 89 ef
> >     RSP: 0018:ffffb55a6591fa80 EFLAGS: 00000202
> >     RAX: 0000000000000000 RBX: ffffb55a6591fac0 RCX: ffffb581e7384000
> >     RDX: ffffb59a9e4e8080 RSI: 0000000000000020 RDI: ffff91d69e8cc000
> >     RBP: ffffb55a6591fb70 R08: 0000000000000002 R09: ffff91d646e12be0
> >     R10: 000000000000006e R11: 0000000000000002 R12: 000000072052d000
> >     R13: ffff91d69e8cc000 R14: ffffb55a6591fbd8 R15: ffff91d69e8cc020
> >     FS:  00007fe10dbda740(0000) GS:ffff92163e480000(0000) knlGS:0000000000000000
> >     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >     CR2: 00007fc041811000 CR3: 00000040d95c8005 CR4: 0000000000770ef0
> >     DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >     DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
> >     PKRU: 55555554
> >     Call Trace:
> >      <IRQ>
> >      ? show_regs+0x67/0x70
> >      ? watchdog_timer_fn+0x1f3/0x280
> >      ? __pfx_watchdog_timer_fn+0x10/0x10
> >      ? __hrtimer_run_queues+0xc8/0x220
> >      ? hrtimer_interrupt+0x10c/0x250
> >      ? __sysvec_apic_timer_interrupt+0x53/0x130
> >      ? sysvec_apic_timer_interrupt+0x7b/0x90
> >      </IRQ>
> >      <TASK>
> >      ? asm_sysvec_apic_timer_interrupt+0x1b/0x20
> >      ? sgx_enclave_restrict_permissions+0xba/0x1f0
> >      ? __pte_offset_map_lock+0x94/0x110
> >      ? sgx_encl_test_and_clear_young_cb+0x40/0x60
> >      sgx_ioctl+0x1ab/0x900
> >      ? do_syscall_64+0x79/0x110
> >      ? apply_to_page_range+0x14/0x20
> >      ? sgx_encl_test_and_clear_young+0x6c/0x80
> >      ? sgx_vma_fault+0x132/0x4f0
> >      __x64_sys_ioctl+0x95/0xd0
> >      x64_sys_call+0x1209/0x20c0
> >      do_syscall_64+0x6d/0x110
> >      ? do_syscall_64+0x79/0x110
> >      ? do_pte_missing+0x2e8/0xcc0
> >      ? __pte_offset_map+0x1c/0x190
> >      ? __handle_mm_fault+0x7b9/0xe60
> >      ? __count_memcg_events+0x70/0x100
> >      ? handle_mm_fault+0x256/0x360
> >      ? do_user_addr_fault+0x3c1/0x860
> >      ? irqentry_exit_to_user_mode+0x67/0x190
> >      ? irqentry_exit+0x3b/0x50
> >      ? exc_page_fault+0x89/0x180
> >      entry_SYSCALL_64_after_hwframe+0x76/0x7e
> >     RIP: 0033:0x7fe10e2ee5cb
> >     Code: 0f 1e fa 48 8b 05 c5 78 0d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 95 78 0d 00 f7 d8 64 89 01 48
> >     RSP: 002b:00007fffb2c75518 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> >     RAX: ffffffffffffffda RBX: 0000000780000000 RCX: 00007fe10e2ee5cb
> >     RDX: 00007fffb2c75520 RSI: 00000000c028a405 RDI: 0000000000000005
> >     RBP: 0000000000000005 R08: 0000000000000000 R09: 00007fffb2c75594
> >     R10: 00007fffb2c755c8 R11: 0000000000000246 R12: 00000000c028a405
> >     R13: 00007fffb2c75520 R14: 0000000780000000 R15: 00007fe10e1a7980
> >      </TASK>
> >      ------------[ end trace ]------------
>
> Could you trim down the trace to only include the relevant part?
>
> E.g., please at least remove the two register dumps at the beginning and
> end of the trace.
>
> Please refer to "Backtraces in commit messages" section in
> Documentation/process/submitting-patches.rst.
>
> > 
> > Signed-off-by: Bojun Zhu <zhubojun.zbj@xxxxxxxxxxxx>
> > ---
> >  arch/x86/kernel/cpu/sgx/ioctl.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> > index b65ab214bdf5..2340a82fa796 100644
> > --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> > @@ -806,6 +806,9 @@ sgx_enclave_restrict_permissions(struct sgx_encl *encl,
> >  		}
> >  
> >  		mutex_unlock(&encl->lock);
> > +
> > +		if (need_resched())
> > +			cond_resched();
> >  	}
> >  
> >  	ret = 0;
> > @@ -1010,6 +1013,9 @@ static long sgx_enclave_modify_types(struct sgx_encl *encl,
> >  		entry->type = page_type;
> >  
> >  		mutex_unlock(&encl->lock);
> > +
> > +		if (need_resched())
> > +			cond_resched();
> >  	}
> >  
> >  	ret = 0;
> > @@ -1156,6 +1162,9 @@ static long sgx_encl_remove_pages(struct sgx_encl *encl,
> >  		kfree(entry);
> >  
> >  		mutex_unlock(&encl->lock);
> > +
> > +		if (need_resched())
> > +			cond_resched();
> >  	}
> > 
>
> You can remove the need_reshced() in all 3 places above but just call
> cond_resched() directly.

If this is the case, then it should be removed also from
sgx_ioc_enclave_add_pages() for the sake of symmetry and related
reasoning of semantic equivalence should be documented to the
commit message (given that something is taken away from code).

BR, Jarkko