linux-kernel - Re: [PATCH v6 11/13] x86/mm/pat: Prepare {reserve, free}

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Date:   Tue, 24 Jul 2018 09:36:41 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Borislav Petkov <bp@...en8.de>, linux-edac@...r.kernel.org,
        x86@...nel.org, hch@....de, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 11/13] x86/mm/pat: Prepare {reserve, free}_memtype()
 for "decoy" addresses


* Dan Williams <dan.j.williams@...el.com> wrote:

> In preparation for using set_memory_uc() instead set_memory_np() for
> isolating poison from speculation, teach the memtype code to sanitize
> physical addresses vs __PHYSICAL_MASK.
> 
> The motivation for using set_memory_uc() for this case is to allow
> ongoing access to persistent memory pages via the pmem-driver +
> memcpy_mcsafe() until the poison is repaired.
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: <linux-edac@...r.kernel.org>
> Cc: <x86@...nel.org>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  arch/x86/mm/pat.c |   16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 1555bd7d3449..6788ffa990f8 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -512,6 +512,17 @@ static int free_ram_pages_type(u64 start, u64 end)
>  	return 0;
>  }
>  
> +static u64 sanitize_phys(u64 address)
> +{
> +	/*
> +	 * When changing the memtype for pages containing poison allow
> +	 * for a "decoy" virtual address (bit 63 clear) passed to
> +	 * set_memory_X(). __pa() on a "decoy" address results in a
> +	 * physical address with it 63 set.
> +	 */
> +	return address & __PHYSICAL_MASK;

s/it/bit

Thanks,

	Ingo