Re: [RFC PATCH v3 1/1] x86/sgx: Explicitly give up the CPU in EDMM's ioctl() to avoid softlockup

[Jarkko Sakkinen]

On Thu May 16, 2024 at 1:29 AM EEST, Haitao Huang wrote:
> On Wed, 15 May 2024 16:55:59 -0500, Haitao Huang  
> <haitao.huang@xxxxxxxxxxxxxxx> wrote:
>
> > On Wed, 15 May 2024 01:55:21 -0500, Bojun Zhu  
> > <zhubojun.zbj@xxxxxxxxxxxx> wrote:
> >
> >> EDMM's ioctl()s support batch operations, which may be
> >> time-consuming. Try to explicitly give up the CPU as the prefix
> >> operation at the every begin of "for loop" in
> >> sgx_enclave_{ modify_types | restrict_permissions | remove_pages}
> >> to give other tasks a chance to run, and avoid softlockup warning.
> >>
> >> Additionally perform pending signals check as the prefix operation,
> >> and introduce sgx_check_signal_and_resched(),
> >> which wraps all the checks.
> >>
> >> 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!
> >>     ...
> >>     RIP: 0010:sgx_enclave_restrict_permissions+0xba/0x1f0
> >>     ...
> >>     Call Trace:
> >>      sgx_ioctl
> >>      __x64_sys_ioctl
> >>      x64_sys_call
> >>      do_syscall_64
> >>      entry_SYSCALL_64_after_hwframe
> >>     ------------[ end trace ]------------
> >>
> >> Signed-off-by: Bojun Zhu <zhubojun.zbj@xxxxxxxxxxxx>
> >> ---
> >>  arch/x86/kernel/cpu/sgx/ioctl.c | 40 +++++++++++++++++++++++----------
> >>  1 file changed, 28 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c  
> >> b/arch/x86/kernel/cpu/sgx/ioctl.c
> >> index b65ab214bdf5..6199f483143e 100644
> >> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> >> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> >> @@ -365,6 +365,20 @@ static int sgx_validate_offset_length(struct  
> >> sgx_encl *encl,
> >>  	return 0;
> >>  }
> >> +/*
> >> + * Check signals and invoke scheduler. Return true for a pending  
> >> signal.
> >> + */
> >> +static bool sgx_check_signal_and_resched(void)
> >> +{
> >> +	if (signal_pending(current))
> >> +		return true;
> >> +
> >> +	if (need_resched())
> >> +		cond_resched();
> >> +
> >> +	return false;
> >> +}
> >> +
> >>  /**
> >>   * sgx_ioc_enclave_add_pages() - The handler for  
> >> %SGX_IOC_ENCLAVE_ADD_PAGES
> >>   * @encl:       an enclave pointer
> >> @@ -409,7 +423,7 @@ static long sgx_ioc_enclave_add_pages(struct  
> >> sgx_encl *encl, void __user *arg)
> >>  	struct sgx_enclave_add_pages add_arg;
> >>  	struct sgx_secinfo secinfo;
> >>  	unsigned long c;
> >> -	int ret;
> >> +	int ret = -ERESTARTSYS;
> >> 	if (!test_bit(SGX_ENCL_CREATED, &encl->flags) ||
> >>  	    test_bit(SGX_ENCL_INITIALIZED, &encl->flags))
> >> @@ -432,15 +446,8 @@ static long sgx_ioc_enclave_add_pages(struct  
> >> sgx_encl *encl, void __user *arg)
> >>  		return -EINVAL;
> >> 	for (c = 0 ; c < add_arg.length; c += PAGE_SIZE) {
> >> -		if (signal_pending(current)) {
> >> -			if (!c)
> >> -				ret = -ERESTARTSYS;
> >> -
> >> +		if (sgx_check_signal_and_resched())
> >>  			break;
> >> -		}
> >
> > ERESTARTSYS is only appropriate if we have not EADDed any pages yet.
> > If we got interrupted in the middle, we should return 0. User space  
> > would check the 'count' returned and decide to recall this ioctl() with  
> > 'offset'  reset to the next page, and adjust length.
>
> NVM, I misread it. ret will be changed to zero in subsequent iteration.
>
> Reviewed-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>

Duh, and I responded too quickly. OK, I revisited the original
patch and yes ret gets reseted. Ignore my previous response ;-)

My tags still hold, sorry.

BR, Jarkko