linux-kernel - [PATCH] x86/sgx: Free backing memory after faulting the enclave page

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Date:   Thu,  4 Nov 2021 01:22:38 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     reinette.chatre@...el.com, tony.luck@...el.com,
        nathaniel@...fian.com, stable@...r.kernel.org,
        Borislav Petkov <bp@...e.de>, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] x86/sgx: Free backing memory after faulting the enclave page

The backing memory was not freed, after loading it back to the SGX
reserved memory. This problem was not prevalent with the systems that
were available at the time when SGX was first upstreamed, as the swapped
memory could grow only up to 128 MB.  However, Icelake Server can have
gigabytes of SGX memory, and thus this has become a real bottleneck.

Free the swap space for other use by calling shmem_truncate_range(),
when a page is faulted back.

Cc: stable@...r.kernel.org
Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
 arch/x86/kernel/cpu/sgx/encl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 001808e3901c..f2d3f2e5028f 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -22,6 +22,7 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
 {
 	unsigned long va_offset = encl_page->desc & SGX_ENCL_PAGE_VA_OFFSET_MASK;
 	struct sgx_encl *encl = encl_page->encl;
+	struct inode *inode = file_inode(encl->backing);
 	struct sgx_pageinfo pginfo;
 	struct sgx_backing b;
 	pgoff_t page_index;
@@ -60,6 +61,9 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
 
 	sgx_encl_put_backing(&b, false);
 
+	/* Free the backing memory. */
+	shmem_truncate_range(inode, PFN_PHYS(page_index), PFN_PHYS(page_index) + PAGE_SIZE - 1);
+
 	return ret;
 }
 
-- 
2.32.0