linux-kernel - Re: [PATCH] x86/sgx: Fix free_cnt counting logic in epc section

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Date:   Wed, 20 Jan 2021 16:36:31 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, haitao.huang@...el.com,
        Kai Huang <kai.huang@...el.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Jia Zhang <zhang.jia@...ux.alibaba.com>
Subject: Re: [PATCH] x86/sgx: Fix free_cnt counting logic in epc section

On Mon, Jan 18, 2021 at 09:33:47PM +0800, Tianjia Zhang wrote:
> Increase `section->free_cnt` in sgx_sanitize_section() is
> more reasonable, which is called in ksgxd kernel thread,
> instead of assigning it to epc section pages number at
> initialization. Although this is unlikely to fail, these
> pages cannot be allocated after initialization, and which
> need to be reset by ksgxd.
> 
> Reported-by: Jia Zhang <zhang.jia@...ux.alibaba.com>
> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>

There is nothing broken in the logic. Convince me otherwise.

I.e. what is exactly broken, and how?

/Jarkko

> ---
>  arch/x86/kernel/cpu/sgx/main.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index c519fc5f6948..9e9a3cf7c00b 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -48,9 +48,10 @@ static void sgx_sanitize_section(struct sgx_epc_section *section)
>  					struct sgx_epc_page, list);
>  
>  		ret = __eremove(sgx_get_epc_virt_addr(page));
> -		if (!ret)
> +		if (!ret) {
>  			list_move(&page->list, &section->page_list);
> -		else
> +			section->free_cnt += 1;
> +		} else
>  			list_move_tail(&page->list, &dirty);
>  
>  		spin_unlock(&section->lock);
> @@ -646,7 +647,6 @@ 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
> 
>