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

[Khalid Aziz <khalid.aziz@oracle.com>]

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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

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