linux-kernel - [PATCH v3 3/5] x86/sgx: Optimize the free_cnt count in sgx_epc

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Date:   Sun, 24 Jan 2021 14:29:05 +0800
From:   Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Shuah Khan <shuah@...nel.org>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jia Zhang <zhang.jia@...ux.alibaba.com>
Cc:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Subject: [PATCH v3 3/5] x86/sgx: Optimize the free_cnt count in sgx_epc_section

`section->free_cnt` represents the free page in sgx_epc_section,
which is assigned once after initialization. In fact, just after the
initialization is completed, the pages are in the `init_laundry_list`
list and cannot be allocated. This needs to be recovered by EREMOVE
of function sgx_sanitize_section() before it can be used as a page
that can be allocated. The sgx_sanitize_section() will be called in
the kernel thread ksgxd.

This patch moves the initialization of `section->free_cnt` from the
initialization function `sgx_setup_epc_section()` to the function
`sgx_sanitize_section()`, and then accumulates the count after the
successful execution of EREMOVE. This seems to be more reasonable,
free_cnt will also truly reflect the allocatable free pages in EPC.

Sined-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Reviewed-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kernel/cpu/sgx/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 4465912174fd..e455ec7b3449 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -48,6 +48,7 @@ static void sgx_sanitize_section(struct sgx_epc_section *section)
 		if (!ret) {
 			spin_lock(&section->lock);
 			list_move(&page->list, &section->page_list);
+			section->free_cnt++;
 			spin_unlock(&section->lock);
 		} else
 			list_move_tail(&page->list, &dirty);
@@ -643,7 +644,6 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
 		list_add_tail(&section->pages[i].list, &section->init_laundry_list);
 	}

-	section->free_cnt = nr_pages;
 	return true;
 }

-- 
2.19.1.3.ge56e4f7