From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Alexey Kardashevskiy <aik@ozlabs.ru>,
David Gibson <david@gibson.dropbear.id.au>
Cc: Alex Williamson <alex.williamson@redhat.com>,
kvm@vger.kernel.org, Eric Auger <eric.auger@redhat.com>,
Paul Mackerras <paulus@samba.org>
Subject: Re: [RFC PATCH kernel] vfio-pci: Allow write combining
Date: Wed, 18 Oct 2017 16:21:12 +0200 [thread overview]
Message-ID: <1508336472.25065.305.camel@kernel.crashing.org> (raw)
In-Reply-To: <da06ea87-6f31-d6b7-eb70-be5915ade62a@ozlabs.ru>
On Wed, 2017-10-18 at 20:00 +1100, Alexey Kardashevskiy wrote:
> >
> > With radix, the HW will honor the G bit set in the guest page tables.
>
>
> I am sure that you know better, Paul just pointed me to this:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/kvm/book3s_64_mmu_radix.c?h=v4.13#n403
It's in the architecture somewhere, if you look at 3.0B in the radix
section about nested radix, there's a table for the nesting of
attributes.
Here you'll see that regardless of the G bit value set by the host,
the HW will use the G bit value set by the guest.
However, we should still provide a way to exploit WC if anything for
things like DPDK.
Cheers,
Ben.
prev parent reply other threads:[~2017-10-18 14:21 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-09 2:50 [RFC PATCH kernel] vfio-pci: Allow write combining Alexey Kardashevskiy
2017-10-10 21:55 ` Alex Williamson
2017-10-11 2:05 ` Alexey Kardashevskiy
2017-10-11 2:42 ` Alex Williamson
2017-10-11 2:56 ` Alexey Kardashevskiy
2017-10-11 15:35 ` Benjamin Herrenschmidt
2017-10-16 5:54 ` Alexey Kardashevskiy
2017-10-16 6:00 ` David Gibson
2017-10-16 7:36 ` Alexey Kardashevskiy
2017-10-16 8:01 ` David Gibson
2017-11-06 5:44 ` Alexey Kardashevskiy
2017-11-14 2:23 ` David Gibson
2017-11-14 2:29 ` Benjamin Herrenschmidt
2017-11-14 16:28 ` Alex Williamson
2017-11-24 4:58 ` Alexey Kardashevskiy
2017-11-29 18:47 ` Alex Williamson
2017-11-30 4:20 ` David Gibson
2017-11-30 20:06 ` Benjamin Herrenschmidt
2017-10-16 8:38 ` Benjamin Herrenschmidt
2017-10-16 11:11 ` Alexey Kardashevskiy
2017-10-18 7:33 ` Benjamin Herrenschmidt
2017-10-18 9:00 ` Alexey Kardashevskiy
2017-10-18 14:21 ` Benjamin Herrenschmidt [this message]
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