Re: [PATCH v5 02/10] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO)

Tycho Andersen
2017-08-15T03:47:21Z

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