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

[Haitao Huang]

On Wed, 15 May 2024 16:55:59 -0500, Haitao Huang  
<haitao.hu...@linux.intel.com> wrote:

On Wed, 15 May 2024 01:55:21 -0500, Bojun Zhu  
<zhubojun....@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....@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.hu...@linux.intel.com>

Thanks
Haitao