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Subject: Re: [PATCH v2 2/4] x86, boot: PUD VA support for physical mapping
 (x86_64)
To: Thomas Garnier <thgarnie@google.com>, "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@suse.de>, Andy Lutomirski <luto@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Kees Cook <keescook@chromium.org>, Stephen Smalley <sds@tycho.nsa.gov>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Toshi Kani <toshi.kani@hpe.com>,
        Alexander Kuleshov <kuleshovmail@gmail.com>,
        Alexander Popov <alpopov@ptsecurity.com>,
        Joerg Roedel <jroedel@suse.de>, Dave Young <dyoung@redhat.com>,
        Baoquan He <bhe@redhat.com>, Mark Salter <msalter@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
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 <1462225276-106993-3-git-send-email-thgarnie@google.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        gthelen@google.com, kernel-hardening@lists.openwall.com
From: Dave Hansen <dave.hansen@linux.intel.com>
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Date: Mon, 2 May 2016 14:58:01 -0700
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On 05/02/2016 02:41 PM, Thomas Garnier wrote:
> Minor change that allows early boot physical mapping of PUD level virtual
> addresses. This change prepares usage of different virtual addresses for
> KASLR memory randomization. It has no impact on default usage.
...
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 89d9747..6adfbce 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -526,10 +526,10 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
>  {
>  	unsigned long pages = 0, next;
>  	unsigned long last_map_addr = end;
> -	int i = pud_index(addr);
> +	int i = pud_index((unsigned long)__va(addr));
>  
>  	for (; i < PTRS_PER_PUD; i++, addr = next) {
> -		pud_t *pud = pud_page + pud_index(addr);
> +		pud_t *pud = pud_page + pud_index((unsigned long)__va(addr));
>  		pmd_t *pmd;
>  		pgprot_t prot = PAGE_KERNEL;

pud_index() is supposed to take a virtual address.  We were passing a
physical address in here, and it all just worked because PAGE_OFFSET is
PUD-aligned.  Now that you are moving PAGE_OFFSET around a bit and not
PUD-aligning it, this breaks.  Right?

Could you spell this out a bit more the changelog?