From: Michael Ellerman <mpe@ellerman.id.au>
To: Ram Pai <linuxram@us.ibm.com>
Cc: ldufour@linux.ibm.com, aik@ozlabs.ru, kvm-ppc@vger.kernel.org,
bharata@linux.ibm.com, sathnaga@linux.vnet.ibm.com,
sukadev@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org,
bauerman@linux.ibm.com, david@gibson.dropbear.id.au
Subject: RE: [RFC PATCH] powerpc/pseries/svm: capture instruction faulting on MMIO access, in sprg0 register
Date: Wed, 22 Jul 2020 22:45:06 +1000 [thread overview]
Message-ID: <87a6zrra5p.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20200722074929.GI7339@oc0525413822.ibm.com>
Ram Pai <linuxram@us.ibm.com> writes:
> On Wed, Jul 22, 2020 at 12:06:06PM +1000, Michael Ellerman wrote:
>> Ram Pai <linuxram@us.ibm.com> writes:
>> > An instruction accessing a mmio address, generates a HDSI fault. This fault is
>> > appropriately handled by the Hypervisor. However in the case of secureVMs, the
>> > fault is delivered to the ultravisor.
>> >
>> > Unfortunately the Ultravisor has no correct-way to fetch the faulting
>> > instruction. The PEF architecture does not allow Ultravisor to enable MMU
>> > translation. Walking the two level page table to read the instruction can race
>> > with other vcpus modifying the SVM's process scoped page table.
>>
>> You're trying to read the guest's kernel text IIUC, that mapping should
>> be stable. Possibly permissions on it could change over time, but the
>> virtual -> real mapping should not.
>
> Actually the code does not capture the address of the instruction in the
> sprg0 register. It captures the instruction itself. So should the mapping
> matter?
Sorry that was talking about reading the instruction by doing the page
walk, not with this patch applied.
cheers
next prev parent reply other threads:[~2020-07-22 12:58 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 8:32 [RFC PATCH] powerpc/pseries/svm: capture instruction faulting on MMIO access, in sprg0 register Ram Pai
2020-07-20 9:39 ` Laurent Dufour
2020-07-20 20:10 ` Segher Boessenkool
2020-07-20 20:24 ` Segher Boessenkool
2020-07-21 7:22 ` Laurent Dufour
2020-07-21 15:00 ` Nicholas Piggin
2020-07-22 2:06 ` Michael Ellerman
2020-07-22 2:23 ` Benjamin Herrenschmidt
2020-07-22 7:49 ` Ram Pai
2020-07-22 12:45 ` Michael Ellerman [this message]
2020-07-24 11:49 ` Michael Ellerman
2020-07-22 5:02 ` Paul Mackerras
2020-07-22 7:42 ` Ram Pai
2020-07-22 7:45 ` Ram Pai
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