From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, paulus@samba.org, agraf@suse.de,
kvm-ppc@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 0/6] Use virtual page class key protection mechanism for speeding up guest page fault
Date: Sun, 29 Jun 2014 21:26:06 +1000 [thread overview]
Message-ID: <1404041166.31323.2.camel@pasglop> (raw)
In-Reply-To: <1404040655-12076-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
On Sun, 2014-06-29 at 16:47 +0530, Aneesh Kumar K.V wrote:
> To achieve the above we use virtual page calss protection mechanism for
> covering (2) and (3). For both the above case we mark the hpte
> valid, but associate the page with virtual page class index 30 and 31.
> The authority mask register is configured such that class index 30 and 31
> will have read/write denied. The above change results in a key fault
> for (2) and (3). This allows us to forward a NO_HPTE fault directly to guest
> without doing the expensive hash pagetable lookup.
So we have a measurable performance benefit (about half a second out of
8) but you didn't explain the drawback here which is to essentially make
it impossible for guests to exploit virtual page class keys, or did you
find a way to still make that possible ?
As it-is, it's not a huge issue for Linux but we might have to care with
other OSes that do care...
Do we have a way in PAPR to signify to the guest that the keys are not
available ?
Cheers,
Ben.
next prev parent reply other threads:[~2014-06-29 11:26 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-29 11:17 [PATCH 0/6] Use virtual page class key protection mechanism for speeding up guest page fault Aneesh Kumar K.V
2014-06-29 11:17 ` [PATCH 1/6] KVM: PPC: BOOK3S: HV: Clear hash pte bits from do_h_enter callers Aneesh Kumar K.V
2014-06-29 11:17 ` [PATCH] KVM: PPC: BOOK3S: HV: Update compute_tlbie_rb to handle 16MB base page Aneesh Kumar K.V
2014-07-02 4:00 ` Paul Mackerras
2014-06-29 11:17 ` [PATCH 2/6] KVM: PPC: BOOK3S: HV: Deny virtual page class key update via h_protect Aneesh Kumar K.V
2014-07-02 4:50 ` Paul Mackerras
2014-07-02 12:12 ` Aneesh Kumar K.V
2014-06-29 11:17 ` [PATCH 3/6] KVM: PPC: BOOK3S: HV: Remove dead code Aneesh Kumar K.V
2014-06-29 11:17 ` [PATCH 4/6] KVM: PPC: BOOK3S: HV: Use new functions for mapping/unmapping hpte in host Aneesh Kumar K.V
2014-07-02 4:28 ` Paul Mackerras
2014-07-02 11:49 ` Aneesh Kumar K.V
2014-06-29 11:17 ` [PATCH 5/6] KVM: PPC: BOOK3S: Use hpte_update_in_progress to track invalid hpte during an hpte update Aneesh Kumar K.V
2014-07-02 5:41 ` Paul Mackerras
2014-07-02 11:57 ` Aneesh Kumar K.V
2014-06-29 11:17 ` [PATCH 6/6] KVM: PPC: BOOK3S: HV: Use virtual page class protection mechanism for host fault and mmio Aneesh Kumar K.V
2014-06-29 11:26 ` Benjamin Herrenschmidt [this message]
2014-06-29 16:57 ` [PATCH 0/6] Use virtual page class key protection mechanism for speeding up guest page fault Aneesh Kumar K.V
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