Re: [RFC PATCH v7 05/16] arm64/mm: Add support for XPFO

[Laura Abbott <labbott@redhat.com>]

On 2/12/19 7:52 AM, Khalid Aziz wrote:
> On 1/23/19 7:24 AM, Konrad Rzeszutek Wilk wrote:
>> On Thu, Jan 10, 2019 at 02:09:37PM -0700, Khalid Aziz wrote:
>>> From: Juerg Haefliger <juerg.haefliger@canonical.com>
>>>
>>> Enable support for eXclusive Page Frame Ownership (XPFO) for arm64 and
>>> provide a hook for updating a single kernel page table entry (which is
>>> required by the generic XPFO code).
>>>
>>> v6: use flush_tlb_kernel_range() instead of __flush_tlb_one()
>>>
>>> CC: linux-arm-kernel@lists.infradead.org
>>> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
>>> Signed-off-by: Tycho Andersen <tycho@docker.com>
>>> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
>>> ---
>>>   arch/arm64/Kconfig     |  1 +
>>>   arch/arm64/mm/Makefile |  2 ++
>>>   arch/arm64/mm/xpfo.c   | 58 ++++++++++++++++++++++++++++++++++++++++++
>>>   3 files changed, 61 insertions(+)
>>>   create mode 100644 arch/arm64/mm/xpfo.c
>>>
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index ea2ab0330e3a..f0a9c0007d23 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -171,6 +171,7 @@ config ARM64
>>>   	select SWIOTLB
>>>   	select SYSCTL_EXCEPTION_TRACE
>>>   	select THREAD_INFO_IN_TASK
>>> +	select ARCH_SUPPORTS_XPFO
>>>   	help
>>>   	  ARM 64-bit (AArch64) Linux support.
>>>   
>>> diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
>>> index 849c1df3d214..cca3808d9776 100644
>>> --- a/arch/arm64/mm/Makefile
>>> +++ b/arch/arm64/mm/Makefile
>>> @@ -12,3 +12,5 @@ KASAN_SANITIZE_physaddr.o	+= n
>>>   
>>>   obj-$(CONFIG_KASAN)		+= kasan_init.o
>>>   KASAN_SANITIZE_kasan_init.o	:= n
>>> +
>>> +obj-$(CONFIG_XPFO)		+= xpfo.o
>>> diff --git a/arch/arm64/mm/xpfo.c b/arch/arm64/mm/xpfo.c
>>> new file mode 100644
>>> index 000000000000..678e2be848eb
>>> --- /dev/null
>>> +++ b/arch/arm64/mm/xpfo.c
>>> @@ -0,0 +1,58 @@
>>> +/*
>>> + * Copyright (C) 2017 Hewlett Packard Enterprise Development, L.P.
>>> + * Copyright (C) 2016 Brown University. All rights reserved.
>>> + *
>>> + * Authors:
>>> + *   Juerg Haefliger <juerg.haefliger@hpe.com>
>>> + *   Vasileios P. Kemerlis <vpk@cs.brown.edu>
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify it
>>> + * under the terms of the GNU General Public License version 2 as published by
>>> + * the Free Software Foundation.
>>> + */
>>> +
>>> +#include <linux/mm.h>
>>> +#include <linux/module.h>
>>> +
>>> +#include <asm/tlbflush.h>
>>> +
>>> +/*
>>> + * Lookup the page table entry for a virtual address and return a pointer to
>>> + * the entry. Based on x86 tree.
>>> + */
>>> +static pte_t *lookup_address(unsigned long addr)
>>> +{
>>> +	pgd_t *pgd;
>>> +	pud_t *pud;
>>> +	pmd_t *pmd;
>>> +
>>> +	pgd = pgd_offset_k(addr);
>>> +	if (pgd_none(*pgd))
>>> +		return NULL;
>>> +
>>> +	pud = pud_offset(pgd, addr);
>>> +	if (pud_none(*pud))
>>> +		return NULL;
>>> +
>>> +	pmd = pmd_offset(pud, addr);
>>> +	if (pmd_none(*pmd))
>>> +		return NULL;
>>> +
>>> +	return pte_offset_kernel(pmd, addr);
>>> +}
>>> +
>>> +/* Update a single kernel page table entry */
>>> +inline void set_kpte(void *kaddr, struct page *page, pgprot_t prot)
>>> +{
>>> +	pte_t *pte = lookup_address((unsigned long)kaddr);
>>> +
>>> +	set_pte(pte, pfn_pte(page_to_pfn(page), prot));
>>
>> Thought on the other hand.. what if the page is PMD? Do you really want
>> to do this?
>>
>> What if 'pte' is NULL?
>>> +}
>>> +
>>> +inline void xpfo_flush_kernel_tlb(struct page *page, int order)
>>> +{
>>> +	unsigned long kaddr = (unsigned long)page_address(page);
>>> +	unsigned long size = PAGE_SIZE;
>>> +
>>> +	flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size);
>>
>> Ditto here. You are assuming it is PTE, but it may be PMD or such.
>> Or worts - the lookup_address could be NULL.
>>
>>> +}
>>> -- 
>>> 2.17.1
>>>
> 
> Hi Konrad,
> 
> This makes sense. x86 version of set_kpte() checks pte for NULL and also
> checks if the page is PMD. Now what you said about adding level to
> lookup_address() for arm makes more sense.
> 
> Can someone with knowledge of arm64 mmu make recommendations here?
> 
> Thanks,
> Khalid
> 

arm64 can't split larger pages and requires everything must be
mapped as pages (see [RFC PATCH v7 08/16] arm64/mm: disable
section/contiguous mappings if XPFO is enabled) . Any
situation where we would get something other than a pte
would be a bug.

Thanks,
Laura