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Date: Mon, 14 Aug 2017 21:47:18 -0600
From: Tycho Andersen <tycho@docker.com>
To: Laura Abbott <labbott@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        kernel-hardening@lists.openwall.com,
        Marco Benatto <marco.antonio.780@gmail.com>,
        Juerg Haefliger <juerg.haefliger@canonical.com>,
        Juerg Haefliger <juerg.haefliger@hpe.com>
Subject: Re: [PATCH v5 02/10] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)
Message-ID: <20170815034718.o6fej2gqkmypxtl2@smitten>
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Hi Laura,

On Mon, Aug 14, 2017 at 03:30:00PM -0700, Laura Abbott wrote:
> On 08/09/2017 01:07 PM, Tycho Andersen wrote:
> > +/* Update a single kernel page table entry */
> > +inline void set_kpte(void *kaddr, struct page *page, pgprot_t prot)
> > +{
> > +	unsigned int level;
> > +	pgprot_t msk_clr;
> > +	pte_t *pte = lookup_address((unsigned long)kaddr, &level);
> > +
> > +	BUG_ON(!pte);
> > +
> > +	switch (level) {
> > +	case PG_LEVEL_4K:
> > +		set_pte_atomic(pte, pfn_pte(page_to_pfn(page), canon_pgprot(prot)));
> > +		break;
> > +	case PG_LEVEL_2M:
> > +		/* We need to check if it's a 2M page or 1GB page before retrieve
> > +		 * pgprot info, as each one will be extracted from a different
> > +		 * page table levels */
> > +		msk_clr = pmd_pgprot(*(pmd_t*)pte);
> > +	case PG_LEVEL_1G: {
> > +		struct cpa_data cpa;
> > +		int do_split;
> > +
> > +		msk_clr = pud_pgprot(*(pud_t*)pte);
> > +
> > +		memset(&cpa, 0, sizeof(cpa));
> > +		cpa.vaddr = kaddr;
> > +		cpa.pages = &page;
> > +		cpa.mask_set = prot;
> > +		cpa.mask_clr = msk_clr;
> > +		cpa.numpages = 1;
> > +		cpa.flags = 0;
> > +		cpa.curpage = 0;
> > +		cpa.force_split = 0;
> > +
> > +
> > +		do_split = try_preserve_large_page(pte, (unsigned long)kaddr, &cpa);
> > +		if (do_split) {
> > +			spin_lock(&cpa_lock);
> > +			BUG_ON(split_large_page(&cpa, pte, (unsigned long)kaddr));
> > +			spin_unlock(&cpa_lock);
> > +		}
> 
> This doesn't work in atomic contexts:
> 
> [   28.263571] BUG: sleeping function called from invalid context at
> mm/page_alloc.c:4048
> [   28.263575] in_atomic(): 1, irqs_disabled(): 1, pid: 2433, name:
> gnome-terminal
> [   28.263576] INFO: lockdep is turned off.
> [   28.263578] irq event stamp: 0
> [   28.263580] hardirqs last  enabled at (0): [<          (null)>]
> (null)
> [   28.263584] hardirqs last disabled at (0): [<ffffffff840af28a>]
> copy_process.part.25+0x62a/0x1e90
> [   28.263587] softirqs last  enabled at (0): [<ffffffff840af28a>]
> copy_process.part.25+0x62a/0x1e90
> [   28.263588] softirqs last disabled at (0): [<          (null)>]
> (null)
> [   28.263591] CPU: 0 PID: 2433 Comm: gnome-terminal Tainted: G        W
> 4.13.0-rc5-xpfo+ #86
> [   28.263592] Hardware name: LENOVO 20BTS1N700/20BTS1N700, BIOS N14ET28W
> (1.06 ) 03/12/2015
> [   28.263593] Call Trace:
> [   28.263598]  dump_stack+0x8e/0xd6
> [   28.263601]  ___might_sleep+0x164/0x250
> [   28.263604]  __might_sleep+0x4a/0x80
> [   28.263607]  __alloc_pages_nodemask+0x2b3/0x3e0
> [   28.263611]  alloc_pages_current+0x6a/0xe0
> [   28.263614]  split_large_page+0x4e/0x360
> [   28.263618]  set_kpte+0x12c/0x150
> [   28.263623]  xpfo_kunmap+0x7e/0xa0
> [   28.263627]  wp_page_copy+0x16e/0x800
> [   28.263631]  do_wp_page+0x9a/0x580
> [   28.263633]  __handle_mm_fault+0xb1c/0x1130
> [   28.263638]  handle_mm_fault+0x178/0x350
> [   28.263641]  __do_page_fault+0x26e/0x510
> [   28.263644]  do_page_fault+0x30/0x80
> [   28.263647]  page_fault+0x28/0x30
> 
> 
> split_large_page calls alloc_page with GFP_KERNEL. switching to
> use GFP_ATOMIC in this path works locally for me.

Oof, thanks. I'll do that for the next version, and also CC x86 in
case they may have better suggestions.

Cheers,

Tycho