From: Khalid Aziz <khalid.aziz@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>,
juergh@gmail.com, jsteckli@amazon.de
Cc: tycho@tycho.ws, ak@linux.intel.com,
torvalds@linux-foundation.org, liran.alon@oracle.com,
keescook@google.com, akpm@linux-foundation.org, mhocko@suse.com,
catalin.marinas@arm.com, will.deacon@arm.com, jmorris@namei.org,
konrad.wilk@oracle.com,
Juerg Haefliger <juerg.haefliger@canonical.com>,
deepa.srinivasan@oracle.com, chris.hyser@oracle.com,
tyhicks@canonical.com, dwmw@amazon.co.uk,
andrew.cooper3@citrix.com, jcm@redhat.com,
boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com,
oao.m.martins@oracle.com, jmattson@google.com,
pradeep.vincent@oracle.com, john.haxby@oracle.com,
tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de,
steven.sistare@oracle.com, labbott@redhat.com, luto@kernel.org,
dave.hansen@intel.com, kernel-hardening@lists.openwall.com,
linux-mm@kvack.org, x86@kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Tycho Andersen <tycho@docker.com>,
Marco Benatto <marco.antonio.780@gmail.com>
Subject: Re: [RFC PATCH v8 03/14] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO)
Date: Thu, 14 Feb 2019 10:13:54 -0700 [thread overview]
Message-ID: <e157e274-1bdf-0987-bfe9-21c9301578ab@oracle.com> (raw)
In-Reply-To: <20190214105631.GJ32494@hirez.programming.kicks-ass.net>
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On 2/14/19 3:56 AM, Peter Zijlstra wrote:
> On Wed, Feb 13, 2019 at 05:01:26PM -0700, Khalid Aziz wrote:
>> static inline void *kmap_atomic(struct page *page)
>> {
>> + void *kaddr;
>> +
>> preempt_disable();
>> pagefault_disable();
>> + kaddr = page_address(page);
>> + xpfo_kmap(kaddr, page);
>> + return kaddr;
>> }
>> #define kmap_atomic_prot(page, prot) kmap_atomic(page)
>>
>> static inline void __kunmap_atomic(void *addr)
>> {
>> + xpfo_kunmap(addr, virt_to_page(addr));
>> pagefault_enable();
>> preempt_enable();
>> }
>
> How is that supposed to work; IIRC kmap_atomic was supposed to be
> IRQ-safe.
>
Ah, the spin_lock in in xpfo_kmap() can be problematic in interrupt
context. I will see if I can fix that.
Juerg, you wrote the original code and understand what you were trying
to do here. If you have ideas on how to tackle this, I would very much
appreciate it.
>> +/* Per-page XPFO house-keeping data */
>> +struct xpfo {
>> + unsigned long flags; /* Page state */
>> + bool inited; /* Map counter and lock initialized */
>
> What's sizeof(_Bool) ? Why can't you use a bit in that flags word?
>
>> + atomic_t mapcount; /* Counter for balancing map/unmap requests */
>> + spinlock_t maplock; /* Lock to serialize map/unmap requests */
>> +};
>
> Without that bool, the structure would be 16 bytes on 64bit, which seems
> like a good number.
>
Patch 11 ("xpfo, mm: remove dependency on CONFIG_PAGE_EXTENSION") cleans
all this up. If the original authors of these two patches, Juerg
Haefliger and Julian Stecklina, are ok with it, I would like to combine
the two patches in one.
>> +void xpfo_kmap(void *kaddr, struct page *page)
>> +{
>> + struct xpfo *xpfo;
>> +
>> + if (!static_branch_unlikely(&xpfo_inited))
>> + return;
>> +
>> + xpfo = lookup_xpfo(page);
>> +
>> + /*
>> + * The page was allocated before page_ext was initialized (which means
>> + * it's a kernel page) or it's allocated to the kernel, so nothing to
>> + * do.
>> + */
>> + if (!xpfo || unlikely(!xpfo->inited) ||
>> + !test_bit(XPFO_PAGE_USER, &xpfo->flags))
>> + return;
>> +
>> + spin_lock(&xpfo->maplock);
>> +
>> + /*
>> + * The page was previously allocated to user space, so map it back
>> + * into the kernel. No TLB flush required.
>> + */
>> + if ((atomic_inc_return(&xpfo->mapcount) == 1) &&
>> + test_and_clear_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags))
>> + set_kpte(kaddr, page, PAGE_KERNEL);
>> +
>> + spin_unlock(&xpfo->maplock);
>> +}
>> +EXPORT_SYMBOL(xpfo_kmap);
>> +
>> +void xpfo_kunmap(void *kaddr, struct page *page)
>> +{
>> + struct xpfo *xpfo;
>> +
>> + if (!static_branch_unlikely(&xpfo_inited))
>> + return;
>> +
>> + xpfo = lookup_xpfo(page);
>> +
>> + /*
>> + * The page was allocated before page_ext was initialized (which means
>> + * it's a kernel page) or it's allocated to the kernel, so nothing to
>> + * do.
>> + */
>> + if (!xpfo || unlikely(!xpfo->inited) ||
>> + !test_bit(XPFO_PAGE_USER, &xpfo->flags))
>> + return;
>> +
>> + spin_lock(&xpfo->maplock);
>> +
>> + /*
>> + * The page is to be allocated back to user space, so unmap it from the
>> + * kernel, flush the TLB and tag it as a user page.
>> + */
>> + if (atomic_dec_return(&xpfo->mapcount) == 0) {
>> + WARN(test_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags),
>> + "xpfo: unmapping already unmapped page\n");
>> + set_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags);
>> + set_kpte(kaddr, page, __pgprot(0));
>> + xpfo_flush_kernel_tlb(page, 0);
>> + }
>> +
>> + spin_unlock(&xpfo->maplock);
>> +}
>> +EXPORT_SYMBOL(xpfo_kunmap);
>
> And these here things are most definitely not IRQ-safe.
>
Got it. I will work on this.
Thanks,
Khalid
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next prev parent reply other threads:[~2019-02-14 17:13 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-14 0:01 [RFC PATCH v8 00/14] Add support for eXclusive Page Frame Ownership Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 01/14] mm: add MAP_HUGETLB support to vm_mmap Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 02/14] x86: always set IF before oopsing from page fault Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 03/14] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Khalid Aziz
2019-02-14 10:56 ` Peter Zijlstra
2019-02-14 16:15 ` Borislav Petkov
2019-02-14 17:19 ` Khalid Aziz
2019-02-14 17:13 ` Khalid Aziz [this message]
2019-02-14 19:08 ` Peter Zijlstra
2019-02-14 19:58 ` Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 04/14] swiotlb: Map the buffer if it was unmapped by XPFO Khalid Aziz
2019-02-14 7:47 ` Christoph Hellwig
2019-02-14 16:56 ` Khalid Aziz
2019-02-14 17:44 ` Christoph Hellwig
2019-02-14 19:48 ` Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 05/14] arm64/mm: Add support for XPFO Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 06/14] xpfo: add primitives for mapping underlying memory Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 07/14] arm64/mm, xpfo: temporarily map dcache regions Khalid Aziz
2019-02-14 15:54 ` Tycho Andersen
2019-02-14 17:29 ` Khalid Aziz
2019-02-14 23:49 ` Tycho Andersen
2019-02-14 0:01 ` [RFC PATCH v8 08/14] arm64/mm: disable section/contiguous mappings if XPFO is enabled Khalid Aziz
2019-02-15 13:09 ` Mark Rutland
2019-02-15 14:47 ` Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 09/14] mm: add a user_virt_to_phys symbol Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 10/14] lkdtm: Add test for XPFO Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 11/14] xpfo, mm: remove dependency on CONFIG_PAGE_EXTENSION Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 12/14] xpfo, mm: optimize spinlock usage in xpfo_kunmap Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 13/14] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) Khalid Aziz
2019-02-14 17:42 ` Dave Hansen
2019-02-14 19:57 ` Khalid Aziz
2019-02-14 0:01 ` [RFC PATCH v8 14/14] xpfo, mm: Optimize XPFO TLB flushes by batching them together Khalid Aziz
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