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Message-ID: <5ADDB2D6.3040703@huawei.com>
Date: Mon, 23 Apr 2018 18:17:58 +0800
From: Xishi Qiu <qiuxishi@huawei.com>
MIME-Version: 1.0
Subject: Re: [RFC] should BIOS change the efi type when we set CONFIG_X86_RESERVE_LOW
 ?
References: <5ACEBB47.3060300@huawei.com>
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To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, "H. Peter Anvin" <hpa@zytor.com>
Cc: yeyunfeng <yeyunfeng@huawei.com>, Wenan Mao <maowenan@huawei.com>, Linux
 MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>

On 2018/4/12 9:49, Xishi Qiu wrote:

> Hi, I find CONFIG_X86_RESERVE_LOW=64 in my system, so trim_low_memory_range()
> will reserve low 64kb memory. But efi_free_boot_services() will free it to
> buddy system again later because BIOS set the type to EFI_BOOT_SERVICES_CODE.
> 
> Here is the log:
> ...
> efi: mem03: type=3, attr=0xf, range=[0x000000000000e000-0x0000000000010000) (0MB
> ...
> 
> 

When call memblock_is_region_reserved(), it will set md->num_pages = 0 if the
memblock region is reserved. But trim_low_memory_range() reserve the region
after efi, so this breaks the logic, and efi_free_boot_services() will free
the pages(efi code/data). That means trim_low_memory_range() has not reserve
the low memory range.

...
efi_reserve_boot_services()
...
trim_low_memory_range()
...
efi_free_boot_services()
...

Shall we move trim_low_memory_range() before efi_reserve_boot_services()?

Thanks,
Xishi Qiu

> .
>