[tip: x86/urgent] x86/sgx: Break up long non-preemptible delays in sgx_vepc_release()

[tip-bot2 for Jack Wang]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     3d7d72a34e05b23e21bafc8bfb861e73c86b31f3
Gitweb:        https://git.kernel.org/tip/3d7d72a34e05b23e21bafc8bfb861e73c86b31f3
Author:        Jack Wang <jinpu.wang@xxxxxxxxx>
AuthorDate:    Wed, 06 Sep 2023 15:17:12 +02:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 06 Sep 2023 23:55:09 +02:00

x86/sgx: Break up long non-preemptible delays in sgx_vepc_release()

On large enclaves we hit the softlockup warning with following call trace:

	xa_erase()
	sgx_vepc_release()
	__fput()
	task_work_run()
	do_exit()

The latency issue is similar to the one fixed in:

  8795359e35bc ("x86/sgx: Silence softlockup detection when releasing large enclaves")

The test system has 64GB of enclave memory, and all is assigned to a single VM.
Release of 'vepc' takes a longer time and causes long latencies, which triggers
the softlockup warning.

Add cond_resched() to give other tasks a chance to run and reduce
latencies, which also avoids the softlockup detector.

[ mingo: Rewrote the changelog. ]

Fixes: 540745ddbc70 ("x86/sgx: Introduce virtual EPC for use by KVM guests")
Reported-by: Yu Zhang <yu.zhang@xxxxxxxxx>
Signed-off-by: Jack Wang <jinpu.wang@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Tested-by: Yu Zhang <yu.zhang@xxxxxxxxx>
Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
Acked-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/cpu/sgx/virt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
index c3e37ea..7aaa365 100644
--- a/arch/x86/kernel/cpu/sgx/virt.c
+++ b/arch/x86/kernel/cpu/sgx/virt.c
@@ -204,6 +204,7 @@ static int sgx_vepc_release(struct inode *inode, struct file *file)
 			continue;
 
 		xa_erase(&vepc->page_array, index);
+		cond_resched();
 	}
 
 	/*
@@ -222,6 +223,7 @@ static int sgx_vepc_release(struct inode *inode, struct file *file)
 			list_add_tail(&epc_page->list, &secs_pages);
 
 		xa_erase(&vepc->page_array, index);
+		cond_resched();
 	}
 
 	/*
@@ -243,6 +245,7 @@ static int sgx_vepc_release(struct inode *inode, struct file *file)
 
 		if (sgx_vepc_free_page(epc_page))
 			list_add_tail(&epc_page->list, &secs_pages);
+		cond_resched();
 	}
 
 	if (!list_empty(&secs_pages))