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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: linux-sgx@vger.kernel.org
Subject: [PATCH for_v23 4/4] x86/sgx: Drop mmap_sem before EEXTENDing an enclave page
Date: Thu, 10 Oct 2019 15:55:30 -0700
Message-ID: <20191010225530.26400-5-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20191010225530.26400-1-sean.j.christopherson@intel.com>

Drop mmap_sem, which needs to be held for read across EADD, prior to
doing EEXTEND on the newly added page to avoid holding mmap_sem for an
extended duration.  EEXTEND doesn't access user pages and holding
encl->lock without mmap_sem is perfectly ok, while EEXTEND is a _slow_
operation, to the point where it operates on 256-byte chunks
instead of 4k pages to maintain a reasonable latency for a single
instruction.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kernel/cpu/sgx/ioctl.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index fd4117f18564..46f2769d16fe 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -403,11 +403,15 @@ static int sgx_encl_add_page(struct sgx_encl *encl,
 	 */
 	ret = radix_tree_insert(&encl->page_tree, PFN_DOWN(encl_page->desc),
 				encl_page);
-	if (ret)
+	if (ret) {
+		up_read(&current->mm->mmap_sem);
 		goto err_out_unlock;
+	}
 
 	ret = __sgx_encl_add_page(encl, encl_page, epc_page, secinfo,
 				  addp->src);
+	up_read(&current->mm->mmap_sem);
+
 	if (ret)
 		goto err_out;
 
@@ -427,7 +431,6 @@ static int sgx_encl_add_page(struct sgx_encl *encl,
 		sgx_mark_page_reclaimable(encl_page->epc_page);
 
 	mutex_unlock(&encl->lock);
-	up_read(&current->mm->mmap_sem);
 	return ret;
 
 err_out:
@@ -437,7 +440,6 @@ static int sgx_encl_add_page(struct sgx_encl *encl,
 err_out_unlock:
 	sgx_encl_shrink(encl, va_page);
 	mutex_unlock(&encl->lock);
-	up_read(&current->mm->mmap_sem);
 
 err_out_free:
 	sgx_free_page(epc_page);
-- 
2.22.0


  parent reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-10 22:55 [PATCH for_v23 0/4] x86/sgx: Fix add page bugs Sean Christopherson
2019-10-10 22:55 ` [PATCH for_v23 1/4] x86/sgx: Pass EADD the kernel's virtual address for the source page Sean Christopherson
2019-10-10 22:55 ` [PATCH for_v23 2/4] x86/sgx: Check the validity of the source page address for EADD Sean Christopherson
2019-10-10 22:55 ` [PATCH for_v23 3/4] x86/sgx: Fix EEXTEND error handling Sean Christopherson
2019-10-10 22:55 ` Sean Christopherson [this message]
2019-10-14 21:03 ` [PATCH for_v23 0/4] x86/sgx: Fix add page bugs Jarkko Sakkinen
2019-10-16 16:39   ` Sean Christopherson
2019-10-17 16:25     ` Jarkko Sakkinen

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