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Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before gues
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts |
Date: |
Tue, 19 Mar 2019 11:03:04 +0000 |
User-agent: |
Mutt/1.11.3 (2019-02-01) |
* Peter Maydell (address@hidden) wrote:
> On Tue, 19 Mar 2019 at 09:40, Dr. David Alan Gilbert
> <address@hidden> wrote:
> > I thought that ROMs would either:
> > a) Be mapped shared from a file but then read-only and unwritten
>
> I don't think we support this at all, do we?
OK, I thought we did somewhere but I might be dreaming it.
> > or
> > b) Be written to during boot - but this wouldn't be main memory, so
> > wouldn't be affected by your shared flag.
>
> The rom code in hw/core/loader.c has two basic cases:
> (1) file is being loaded to something that is really a pure ROM:
> in this case, on first reset we will write it to the backing RAMBlock
> but we will not bother to do so in future
> (2) file is being loaded to something that is not a pure ROM:
> this could be either real RAM (eg if a file is loaded via -kernel
> or the 'generic loader' device), or a flash device, for instance.
> In this case we will reload the backing RAMBlock with the file
> contents on every reset, because the guest might have changed its
> contents.
> (There's also "file is provided via the fw_cfg device" but that's
> not relevant here.)
>
> I didn't think migration distinguished between "main memory"
> and any other kind of RAMBlock-backed memory ?
In Yury's case there's a distinction between RAMBlock's that are mapped
with RAM_SHARED (which normally ends up as MAP_SHARED) and all others.
You can set that for main memory by using -numa to specify a memdev
that's backed by a file and has the share=on property.
On x86 the ROMs end up as separate RAMBlock's that aren't affected
by that -numa/share=on - so they don't fight Yury's trick.
Dave
> thanks
> -- PMM
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Yury Kotov, 2019/03/14
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Jia He, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Dr. David Alan Gilbert, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Peter Maydell, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Peter Maydell, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Dr. David Alan Gilbert, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Igor Mammedov, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Peter Maydell, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Igor Mammedov, 2019/03/19
- Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Yury Kotov, 2019/03/21
Re: [Qemu-devel] [RFC PATCH] QEMU may write to system_memory before guest starts, Yury Kotov, 2019/03/19