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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.

      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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