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Re: [Xen-devel] {xen, dom0}_vga_console_info.u.vesa_lfb.lfb_base field too small
- To: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Mon, 6 May 2019 10:04:42 +0200
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- Delivery-date: Mon, 06 May 2019 08:05:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 05/05/2019 15:27, Marek Marczykowski-Górecki wrote:
> Hi,
>
> I have a machine that allocate vesa LFB above 4GB, as reported by UEFI
> GOP. At 0x4000000000 to be specific.
> vga_console_info.u.vesa_lfb.lfb_base is a 32bit field, so it gets
> truncated, leading to all kind of memory corruptions when something
> writes there.
> If that would be only about Xen, that wouldn't be that bad, but
> unfortunately exactly the same structure is used as an interface for
> dom0 start info (at least PV one).
> My only idea is to introduce yet another entry in *_vga_console_info.u
> union (efi_lfb64?) with a 64bit lfb_base field. And mark it in
> video_type (XEN_VGATYPE_EFI_LFB64?). But I'm not sure how non-patched
> Linux (or other supported OSes) would respond to this. xen_init_vga() in
> Linux doesn't seem to bail on unknown video_type, so it may be fragile.
>
> Any better ideas?
In Linux kernel the screen_info structure has ext_lfb_base for that
purpose (it contains the upper 32 bits of lfb_base).
We could add a similar member to Xen's dom0_vga_console_info.u.vesa_lfb
and let the kernel detect its presence by using the value of
start_info.console.dom0.info_size - this wouldn't require a new video
type and old kernels would run as today. The same scheme is used for
gbl_caps and mode_attrs already.
Releated to that: I assume the comment in xen.h regarding lfb_base and
lfb_size being in units of 64kB is wrong and should be removed?
Juergen
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