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From: Matthew Wilcox <willy@infradead.org>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: linux-nvdimm@lists.01.org,
	Alex Williamson <alex.williamson@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	kvm@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H . Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Liran Alon <liran.alon@oracle.com>,
	Nikita Leshenko <nikita.leshchenko@oracle.com>,
	Barret Rhoden <brho@google.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH RFC 01/10] mm: Add pmd support for _PAGE_SPECIAL
Date: Mon, 3 Feb 2020 13:34:42 -0800	[thread overview]
Message-ID: <20200203213442.GK8731@bombadil.infradead.org> (raw)
In-Reply-To: <20200110190313.17144-2-joao.m.martins@oracle.com>

On Fri, Jan 10, 2020 at 07:03:04PM +0000, Joao Martins wrote:
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -293,6 +293,15 @@ static inline int pgd_devmap(pgd_t pgd)
>  {
>  	return 0;
>  }
> +#endif
> +
> +#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
> +static inline int pmd_special(pmd_t pmd)
> +{
> +	return !!(pmd_flags(pmd) & _PAGE_SPECIAL);
> +}
> +#endif

The ifdef/endif don't make much sense here; x86 does have PTE_SPECIAL,
and this is an x86 header file, so that can be assumed.

> +++ b/mm/gup.c
> @@ -2079,6 +2079,9 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>  		return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
>  	}
>  
> +	if (pmd_special(orig))
> +		return 0;

Here, you're calling it unconditionally.  I think you need a pmd_special()
conditionally defined in include/asm-generic/pgtable.h

+#ifndef CONFIG_ARCH_HAS_PTE_SPECIAL
+static inline bool pmd_special(pmd_t pmd)
+{
+	return false;
+}
+#endif

(oh, and plese use bool instead of int; I know that's different from
pte_special(), but pte_special() predates bool and nobody's done the work
to convert it yet)

> +++ b/mm/huge_memory.c
> @@ -791,6 +791,8 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  	entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
>  	if (pfn_t_devmap(pfn))
>  		entry = pmd_mkdevmap(entry);
> +	else if (pfn_t_special(pfn))
> +		entry = pmd_mkspecial(entry);

Again, we'll need a generic one.

> @@ -823,8 +825,7 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write)
>  	 * but we need to be consistent with PTEs and architectures that
>  	 * can't support a 'special' bit.
>  	 */
> -	BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
> -			!pfn_t_devmap(pfn));
> +	BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));

Should that rather be ...

+	BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
+			!pfn_t_devmap(pfn) && !pfn_t_special(pfn));

I also think this comment needs adjusting:

        /*
         * There is no pmd_special() but there may be special pmds, e.g.
         * in a direct-access (dax) mapping, so let's just replicate the
         * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here.
         */

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  reply	other threads:[~2020-02-03 21:34 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-10 19:03 [PATCH RFC 00/10] device-dax: Support devices without PFN metadata Joao Martins
2020-01-10 19:03 ` [PATCH RFC 01/10] mm: Add pmd support for _PAGE_SPECIAL Joao Martins
2020-02-03 21:34   ` Matthew Wilcox [this message]
2020-02-04 16:14     ` Joao Martins
2020-01-10 19:03 ` [PATCH RFC 02/10] mm: Handle pmd entries in follow_pfn() Joao Martins
2020-02-03 21:37   ` Matthew Wilcox
2020-02-04 16:17     ` Joao Martins
2020-01-10 19:03 ` [PATCH RFC 03/10] mm: Add pud support for _PAGE_SPECIAL Joao Martins
2020-01-10 19:03 ` [PATCH RFC 04/10] mm: Handle pud entries in follow_pfn() Joao Martins
2020-01-10 19:03 ` [PATCH RFC 05/10] device-dax: Do not enforce MADV_DONTFORK on mmap() Joao Martins
2020-01-10 19:03 ` [PATCH RFC 06/10] device-dax: Introduce pfn_flags helper Joao Martins
2020-01-10 19:03 ` [PATCH RFC 07/10] device-dax: Add support for PFN_SPECIAL flags Joao Martins
2020-01-10 19:03 ` [PATCH RFC 08/10] dax/pmem: Add device-dax support for PFN_MODE_NONE Joao Martins
2020-01-10 19:03 ` [PATCH RFC 09/10] vfio/type1: Use follow_pfn for VM_FPNMAP VMAs Joao Martins
     [not found]   ` <20200207210831.GA31015@ziepe.ca>
2020-02-11 16:23     ` Joao Martins
2020-01-10 19:03 ` [PATCH RFC 10/10] nvdimm/e820: add multiple namespaces support Joao Martins
2020-02-04 15:28   ` Barret Rhoden
2020-02-04 16:44     ` Dan Williams
2020-02-04 18:20       ` Barret Rhoden
2020-02-04 19:24         ` Joao Martins
2020-02-04 21:43         ` Dan Williams
2020-02-04 21:57           ` Barret Rhoden
2020-02-04  1:24 ` [PATCH RFC 00/10] device-dax: Support devices without PFN metadata Dan Williams
2020-02-04 19:07   ` Joao Martins

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