From: Paolo Bonzini <pbonzini@redhat.com>
To: Laszlo Ersek <lersek@redhat.com>,
"Kinney, Michael D" <michael.d.kinney@intel.com>,
"rfc@edk2.groups.io" <rfc@edk2.groups.io>,
"Yao, Jiewen" <jiewen.yao@intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
"devel@edk2.groups.io" <devel@edk2.groups.io>,
qemu devel list <qemu-devel@nongnu.org>,
Igor Mammedov <imammedo@redhat.com>,
"Chen, Yingwen" <yingwen.chen@intel.com>,
"Nakajima, Jun" <jun.nakajima@intel.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Joao Marcal Lemos Martins <joao.m.martins@oracle.com>,
Phillip Goerl <phillip.goerl@oracle.com>
Subject: Re: [edk2-rfc] [edk2-devel] CPU hotplug using SMM with QEMU+OVMF
Date: Thu, 22 Aug 2019 20:51:09 +0200 [thread overview]
Message-ID: <c96fc875-ac07-b33c-e752-35cb65fa0e5e@redhat.com> (raw)
In-Reply-To: <3ca65433-8aed-57d4-7f18-a2a2718a6ffe@redhat.com>
On 22/08/19 20:29, Laszlo Ersek wrote:
> On 08/22/19 08:18, Paolo Bonzini wrote:
>> On 21/08/19 22:17, Kinney, Michael D wrote:
>>> DMA protection of memory ranges is a chipset feature. For the current
>>> QEMU implementation, what ranges of memory are guaranteed to be
>>> protected from DMA? Is it only A/B seg and TSEG?
>>
>> Yes.
>
> This thread (esp. Jiewen's and Mike's messages) are the first time that
> I've heard about the *existence* of such RAM ranges / the chipset
> feature. :)
>
> Out of interest (independently of virtualization), how is a general
> purpose OS informed by the firmware, "never try to set up DMA to this
> RAM area"? Is this communicated through ACPI _CRS perhaps?
>
> ... Ah, almost: ACPI 6.2 specifies _DMA, in "6.2.4 _DMA (Direct Memory
> Access)". It writes,
>
> For example, if a platform implements a PCI bus that cannot access
> all of physical memory, it has a _DMA object under that PCI bus that
> describes the ranges of physical memory that can be accessed by
> devices on that bus.
>
> Sorry about the digression, and also about being late to this thread,
> continually -- I'm primarily following and learning.
It's much simpler: these ranges are not in e820, for example
kernel: BIOS-e820: [mem 0x0000000000059000-0x000000000008bfff] usable
kernel: BIOS-e820: [mem 0x000000000008c000-0x00000000000fffff] reserved
The ranges are not special-cased in any way by QEMU. Simply, AB-segs
and TSEG RAM are not part of the address space except when in SMM.
Therefore, DMA to those ranges ends up respectively to low VGA RAM[1]
and to the bit bucket. When AB-segs are open, for example, DMA to that
area becomes possible.
Paolo
[1] old timers may remember DEF SEG=&HB800: BLOAD "foo.img",0. It still
works with some disk device models.
next prev parent reply other threads:[~2019-08-22 18:51 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-13 14:16 CPU hotplug using SMM with QEMU+OVMF Laszlo Ersek
2019-08-13 16:09 ` Laszlo Ersek
2019-08-13 16:18 ` Laszlo Ersek
2019-08-14 13:20 ` Yao, Jiewen
2019-08-14 14:04 ` Paolo Bonzini
2019-08-15 9:55 ` Yao, Jiewen
2019-08-15 16:04 ` Paolo Bonzini
2019-08-15 15:00 ` [edk2-devel] " Laszlo Ersek
2019-08-15 16:16 ` Igor Mammedov
2019-08-15 16:21 ` Paolo Bonzini
2019-08-16 2:46 ` Yao, Jiewen
2019-08-16 7:20 ` Paolo Bonzini
2019-08-16 7:49 ` Yao, Jiewen
2019-08-16 20:15 ` Laszlo Ersek
2019-08-16 22:19 ` Alex Williamson
2019-08-17 0:20 ` Yao, Jiewen
2019-08-18 19:50 ` Paolo Bonzini
2019-08-18 23:00 ` Yao, Jiewen
2019-08-19 14:10 ` Paolo Bonzini
2019-08-21 12:07 ` Laszlo Ersek
2019-08-21 15:48 ` [edk2-rfc] " Michael D Kinney
2019-08-21 17:05 ` Paolo Bonzini
2019-08-21 17:25 ` Michael D Kinney
2019-08-21 17:39 ` Paolo Bonzini
2019-08-21 20:17 ` Michael D Kinney
2019-08-22 6:18 ` Paolo Bonzini
2019-08-22 18:29 ` Laszlo Ersek
2019-08-22 18:51 ` Paolo Bonzini [this message]
2019-08-23 14:53 ` Laszlo Ersek
2019-08-22 20:13 ` Michael D Kinney
2019-08-22 17:59 ` Laszlo Ersek
2019-08-22 18:43 ` Paolo Bonzini
2019-08-22 20:06 ` Michael D Kinney
2019-08-22 22:18 ` Paolo Bonzini
2019-08-22 22:32 ` Michael D Kinney
2019-08-22 23:11 ` Paolo Bonzini
2019-08-23 1:02 ` Michael D Kinney
2019-08-23 5:00 ` Yao, Jiewen
2019-08-23 15:25 ` Michael D Kinney
2019-08-24 1:48 ` Yao, Jiewen
2019-08-27 18:31 ` Igor Mammedov
2019-08-29 17:01 ` Laszlo Ersek
2019-08-30 14:48 ` Igor Mammedov
2019-08-30 18:46 ` Laszlo Ersek
2019-09-02 8:45 ` Igor Mammedov
2019-09-02 19:09 ` Laszlo Ersek
2019-09-03 14:53 ` [Qemu-devel] " Igor Mammedov
2019-09-03 17:20 ` Laszlo Ersek
2019-09-04 9:52 ` imammedo
2019-09-05 13:08 ` Laszlo Ersek
2019-09-05 15:45 ` Igor Mammedov
2019-09-05 15:49 ` [PATCH] q35: lpc: allow to lock down 128K RAM at default SMBASE address Igor Mammedov
2019-09-09 19:15 ` Laszlo Ersek
2019-09-09 19:20 ` Laszlo Ersek
2019-09-10 15:58 ` Igor Mammedov
2019-09-11 17:30 ` Laszlo Ersek
2019-09-17 13:11 ` [edk2-devel] " Igor Mammedov
2019-09-17 14:38 ` [staging/branch]: CdePkg - C Development Environment Package Minnow Ware
2019-08-26 15:30 ` [edk2-rfc] [edk2-devel] CPU hotplug using SMM with QEMU+OVMF Laszlo Ersek
2019-08-27 16:23 ` Igor Mammedov
2019-08-27 20:11 ` Laszlo Ersek
2019-08-28 12:01 ` Igor Mammedov
2019-08-29 16:25 ` Laszlo Ersek
2019-08-30 13:49 ` [Qemu-devel] " Igor Mammedov
2019-08-22 17:53 ` Laszlo Ersek
2019-08-16 20:00 ` Laszlo Ersek
2019-08-15 16:07 ` Igor Mammedov
2019-08-15 16:24 ` Paolo Bonzini
2019-08-16 7:42 ` Igor Mammedov
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