linux-kernel - Re: [PATCH v2] x86/efi: unconditionally hold the whole low-1MB memory regions

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Date:   Mon, 31 May 2021 15:13:58 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     lijiang <lijiang@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, kexec@...ts.infradead.org,
        ardb@...nel.org, dvhart@...radead.org, andy@...radead.org,
        tglx@...utronix.de, Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        luto@...capital.net, Baoquan He <bhe@...hat.com>,
        Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v2] x86/efi: unconditionally hold the whole low-1MB
 memory regions

On Mon, May 31, 2021 at 07:00:59PM +0800, lijiang wrote:
> Thank you for the information, Boris and Mike.
> 
> BTW: I just noticed that Mike's patch is incorrect, maybe it's a typo:
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index 7850111008a8b..e262ca858787f 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -450,6 +450,18 @@ void __init efi_free_boot_services(void)
> size -= rm_size;
> }
> + /*
> + * Don't free memory under 1M for two reasons:
> + * - BIOS might clobber it
> + * - Crash kernel needs it to be reserved
> + */
> + if (start + size < SZ_1M)
> + continue;
> + if (start < SZ_1M) {
> + size -= (start - SZ_1M);
> ^^^^^^^^^^^^^^^^^^^^^^^^
> 
> It looks like: size -= (SZ_1M - start);

Right, thanks!

> + start = SZ_1M;
> + }
> +
> memblock_free_late(start, size);
> }
> 
> Mike's patch link:
> https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/commit/?h=x86/
> reservelow&id=479fb34676ac448529b605854cf48c007e796ccd
 
-- 
Sincerely yours,
Mike.