linux-kernel - Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation

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Message-ID: <YsRZ8V8mQ+HM31D6@arm.com>
Date:   Tue, 5 Jul 2022 16:34:09 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        "guanghui.fgh" <guanghuifeng@...ux.alibaba.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        baolin.wang@...ux.alibaba.com, akpm@...ux-foundation.org,
        david@...hat.com, jianyong.wu@....com, james.morse@....com,
        quic_qiancai@...cinc.com, christophe.leroy@...roup.eu,
        jonathan@...ek.ca, mark.rutland@....com,
        thunder.leizhen@...wei.com, anshuman.khandual@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        geert+renesas@...der.be, linux-mm@...ck.org,
        yaohongbo@...ux.alibaba.com, alikernel-developer@...ux.alibaba.com
Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance
 degradation

On Tue, Jul 05, 2022 at 06:02:02PM +0300, Mike Rapoport wrote:
> +void __init remap_crashkernel(void)
> +{
> +#ifdef CONFIG_KEXEC_CORE
> +	phys_addr_t start, end, size;
> +	phys_addr_t aligned_start, aligned_end;
> +
> +	if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE))
> +	    return;
> +
> +	if (!crashk_res.end)
> +	    return;
> +
> +	start = crashk_res.start & PAGE_MASK;
> +	end = PAGE_ALIGN(crashk_res.end);
> +
> +	aligned_start = ALIGN_DOWN(crashk_res.start, PUD_SIZE);
> +	aligned_end = ALIGN(end, PUD_SIZE);
> +
> +	/* Clear PUDs containing crash kernel memory */
> +	unmap_hotplug_range(__phys_to_virt(aligned_start),
> +			    __phys_to_virt(aligned_end), false, NULL);

What I don't understand is what happens if there's valid kernel data
between aligned_start and crashk_res.start (or the other end of the
range).

-- 
Catalin