From: Paolo Bonzini <pbonzini@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>, kvm <kvm@vger.kernel.org>,
"Joel Schopp" <joel.schopp@amd.com>
Subject: Re: [PATCH v2] KVM: SVM: Sync g_pat with guest-written PAT value
Date: Tue, 21 Apr 2015 14:12:44 +0200 [thread overview]
Message-ID: <55363EBC.8000202@redhat.com> (raw)
In-Reply-To: <55363B04.20108@siemens.com>
On 21/04/2015 13:56, Jan Kiszka wrote:
> > Basically it's an optimization. The guest can set the UC memory type on
> > PCI BARs that are actually backed by RAM in QEMU, and then accesses to
> > these BARs will be unnecessarily slow. It would be particularly bad if,
> > for example, access to ivshmem were slowed down because the guest PAT
> > says the memory is uncacheable.
>
> ivshmem is pv anyway - why shouldn't the guest driver take this room for
> optimization into account and ask for a cached mapping?
>
> Is that that only use case?
I guess a frame buffer would be affected as well, though probably the
guest would set it to WC so it's less bad.
Paolo
next prev parent reply other threads:[~2015-04-21 12:12 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-13 5:16 KVM: How does is PAT emulation supposed to work? Jan Kiszka
2015-04-13 6:58 ` [RFC][PATCH] KVM: SVM: Sync g_pat with guest-written PAT value Jan Kiszka
2015-04-17 16:59 ` Radim Krčmář
2015-04-20 16:14 ` Radim Krčmář
2015-04-20 17:16 ` Radim Krčmář
2015-04-20 17:21 ` Jan Kiszka
2015-04-20 17:33 ` Radim Krčmář
2015-04-20 17:37 ` Jan Kiszka
2015-04-20 17:45 ` Jan Kiszka
2015-04-20 18:33 ` Radim Krčmář
2015-04-20 18:41 ` Jan Kiszka
2015-04-21 12:10 ` Radim Krčmář
2015-04-21 12:11 ` Paolo Bonzini
2015-04-20 17:22 ` Radim Krčmář
2015-04-20 17:25 ` [PATCH v2] " Jan Kiszka
2015-04-20 17:35 ` Radim Krčmář
2015-04-21 11:09 ` Paolo Bonzini
2015-04-21 11:25 ` Jan Kiszka
2015-04-21 11:32 ` Paolo Bonzini
2015-04-21 11:56 ` Jan Kiszka
2015-04-21 12:12 ` Paolo Bonzini [this message]
2015-04-21 12:21 ` Radim Krčmář
2015-05-24 15:28 ` Jan Kiszka
2016-02-09 19:25 ` Jan Kiszka
2015-04-17 16:43 ` KVM: How does is PAT emulation supposed to work? Radim Krčmář
2015-04-17 17:12 ` Jan Kiszka
2015-04-17 20:28 ` Radim Krčmář
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