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SubjectRe: [RFC PATCH v3 1/1] x86/sgx: Explicitly give up the CPU in EDMM's ioctl() to avoid softlockup
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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@linux.intel.com> wrote:
>
> > On Wed, 15 May 2024 01:55:21 -0500, Bojun Zhu
> > <zhubojun.zbj@antgroup.com> 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@antgroup.com>
> >> ---
> >> 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@linux.intel.com>

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

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