From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linuxppc-dev@lists.ozlabs.org,
David Gibson <david@gibson.dropbear.id.au>,
Alexander Graf <agraf@suse.de>, Paul Mackerras <paulus@samba.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm-ppc@vger.kernel.org
Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling
Date: Wed, 19 Jun 2013 13:17:16 +1000 [thread overview]
Message-ID: <51C122BC.8060107@ozlabs.ru> (raw)
In-Reply-To: <1371357560.21896.120.camel@pasglop>
On 06/16/2013 02:39 PM, Benjamin Herrenschmidt wrote:
>> static pte_t kvmppc_lookup_pte(pgd_t *pgdir, unsigned long hva, bool writing,
>> - unsigned long *pte_sizep)
>> + unsigned long *pte_sizep, bool do_get_page)
>> {
>> pte_t *ptep;
>> unsigned int shift = 0;
>> @@ -135,6 +136,14 @@ static pte_t kvmppc_lookup_pte(pgd_t *pgdir, unsigned long hva, bool writing,
>> if (!pte_present(*ptep))
>> return __pte(0);
>>
>> + /*
>> + * Put huge pages handling to the virtual mode.
>> + * The only exception is for TCE list pages which we
>> + * do need to call get_page() for.
>> + */
>> + if ((*pte_sizep > PAGE_SIZE) && do_get_page)
>> + return __pte(0);
>> +
>> /* wait until _PAGE_BUSY is clear then set it atomically */
>> __asm__ __volatile__ (
>> "1: ldarx %0,0,%3\n"
>> @@ -148,6 +157,18 @@ static pte_t kvmppc_lookup_pte(pgd_t *pgdir, unsigned long hva, bool writing,
>> : "cc");
>>
>> ret = pte;
>> + if (do_get_page && pte_present(pte) && (!writing || pte_write(pte))) {
>> + struct page *pg = NULL;
>> + pg = realmode_pfn_to_page(pte_pfn(pte));
>> + if (realmode_get_page(pg)) {
>> + ret = __pte(0);
>> + } else {
>> + pte = pte_mkyoung(pte);
>> + if (writing)
>> + pte = pte_mkdirty(pte);
>> + }
>> + }
>> + *ptep = pte; /* clears _PAGE_BUSY */
>>
>> return ret;
>> }
>
> So now you are adding the clearing of _PAGE_BUSY that was missing for
> your first patch, except that this is not enough since that means that
> in the "emulated" case (ie, !do_get_page) you will in essence return
> and then use a PTE that is not locked without any synchronization to
> ensure that the underlying page doesn't go away... then you'll
> dereference that page.
>
> So either make everything use speculative get_page, or make the emulated
> case use the MMU notifier to drop the operation in case of collision.
>
> The former looks easier.
>
> Also, any specific reason why you do:
>
> - Lock the PTE
> - get_page()
> - Unlock the PTE
>
> Instead of
>
> - Read the PTE
> - get_page_unless_zero
> - re-check PTE
>
> Like get_user_pages_fast() does ?
>
> The former will be two atomic ops, the latter only one (faster), but
> maybe you have a good reason why that can't work...
If we want to set "dirty" and "young" bits for pte then I do not know how
to avoid _PAGE_BUSY.
--
Alexey
next prev parent reply other threads:[~2013-06-19 3:17 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-05 6:11 [PATCH 0/4 v3] KVM: PPC: IOMMU in-kernel handling Alexey Kardashevskiy
2013-06-05 6:11 ` [PATCH 1/4] KVM: PPC: Add support for multiple-TCE hcalls Alexey Kardashevskiy
2013-06-16 4:20 ` Benjamin Herrenschmidt
2013-06-16 22:06 ` Alexander Graf
2013-06-17 7:55 ` Alexey Kardashevskiy
2013-06-17 8:02 ` Alexander Graf
2013-06-17 8:34 ` Alexey Kardashevskiy
2013-06-17 8:40 ` Alexander Graf
2013-06-17 8:51 ` Alexey Kardashevskiy
2013-06-17 10:46 ` Alexander Graf
2013-06-17 10:48 ` Alexander Graf
2013-06-17 8:37 ` Benjamin Herrenschmidt
2013-06-17 8:42 ` Alexander Graf
2013-06-05 6:11 ` [PATCH 2/4] powerpc: Prepare to support kernel handling of IOMMU map/unmap Alexey Kardashevskiy
2013-06-16 4:26 ` Benjamin Herrenschmidt
2013-06-16 4:31 ` Benjamin Herrenschmidt
2013-06-17 9:17 ` Alexey Kardashevskiy
2013-06-05 6:11 ` [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling Alexey Kardashevskiy
2013-06-16 4:39 ` Benjamin Herrenschmidt
2013-06-19 3:17 ` Alexey Kardashevskiy [this message]
2013-06-16 22:25 ` Alexander Graf
2013-06-16 22:39 ` Benjamin Herrenschmidt
2013-06-17 3:13 ` Alex Williamson
2013-06-17 3:56 ` Benjamin Herrenschmidt
2013-06-18 2:32 ` Alex Williamson
2013-06-18 4:38 ` Benjamin Herrenschmidt
2013-06-18 14:48 ` Alex Williamson
2013-06-18 21:58 ` Benjamin Herrenschmidt
2013-06-19 3:35 ` Rusty Russell
2013-06-19 4:59 ` Benjamin Herrenschmidt
2013-06-19 9:58 ` Alexander Graf
2013-06-19 14:50 ` Benjamin Herrenschmidt
2013-06-19 15:49 ` Alex Williamson
2013-06-20 4:58 ` Alexey Kardashevskiy
2013-06-20 5:28 ` David Gibson
2013-06-20 7:47 ` Benjamin Herrenschmidt
2013-06-20 8:48 ` Alexey Kardashevskiy
2013-06-20 14:55 ` Alex Williamson
2013-06-22 8:25 ` Alexey Kardashevskiy
2013-06-22 12:03 ` David Gibson
2013-06-22 14:28 ` Alex Williamson
2013-06-24 3:52 ` David Gibson
2013-06-24 4:41 ` Alex Williamson
2013-06-27 11:01 ` David Gibson
2013-06-22 23:28 ` Benjamin Herrenschmidt
2013-06-24 3:54 ` David Gibson
2013-06-24 3:58 ` Benjamin Herrenschmidt
2013-06-05 6:11 ` [PATCH 4/4] KVM: PPC: Add hugepage " Alexey Kardashevskiy
2013-06-16 4:46 ` Benjamin Herrenschmidt
2013-06-17 16:35 ` Paolo Bonzini
2013-06-12 3:14 ` [PATCH 0/4 v3] KVM: PPC: " Benjamin Herrenschmidt
-- strict thread matches above, loose matches on Subject: below --
2013-05-21 3:06 [PATCH 0/4 v2] " Alexey Kardashevskiy
2013-05-21 3:06 ` [PATCH 3/4] KVM: PPC: Add support for " Alexey Kardashevskiy
2013-05-22 21:06 ` Scott Wood
2013-05-25 2:45 ` David Gibson
2013-05-27 2:44 ` Alexey Kardashevskiy
2013-05-28 17:45 ` Scott Wood
2013-05-28 23:30 ` Alexey Kardashevskiy
2013-05-28 23:35 ` Scott Wood
2013-05-29 0:12 ` Alexey Kardashevskiy
2013-05-29 20:05 ` Scott Wood
2013-05-29 23:10 ` Alexey Kardashevskiy
2013-05-29 23:14 ` Scott Wood
2013-05-29 23:29 ` Alexey Kardashevskiy
2013-05-29 23:32 ` Scott Wood
2013-05-27 10:23 ` Paolo Bonzini
2013-05-27 14:26 ` Alexey Kardashevskiy
2013-05-27 14:41 ` Paolo Bonzini
2013-05-28 16:32 ` Scott Wood
2013-05-29 0:20 ` Alexey Kardashevskiy
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