Re: [PATCH 2/2] xen/x86/pvh: copy ACPI tables to Dom0 instead of mapping

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 15 May 2023, Stefano Stabellini wrote:
> On Mon, 15 May 2023, Roger Pau Monné wrote:
> > On Fri, May 12, 2023 at 06:17:20PM -0700, Stefano Stabellini wrote:
> > > From: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> > > 
> > > Mapping the ACPI tables to Dom0 PVH 1:1 leads to memory corruptions of
> > > the tables in the guest. Instead, copy the tables to Dom0.
> > > 
> > > This is a workaround.
> > > 
> > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> > > ---
> > > As mentioned in the cover letter, this is a RFC workaround as I don't
> > > know the cause of the underlying problem. I do know that this patch
> > > solves what would be otherwise a hang at boot when Dom0 PVH attempts to
> > > parse ACPI tables.
> > 
> > I'm unsure how safe this is for native systems, as it's possible for
> > firmware to modify the data in the tables, so copying them would
> > break that functionality.
> > 
> > I think we need to get to the root cause that triggers this behavior
> > on QEMU.  Is it the table checksum that fail, or something else?  Is
> > there an error from Linux you could reference?
> 
> I agree with you but so far I haven't managed to find a way to the root
> of the issue. Here is what I know. These are the logs of a successful
> boot using this patch:
> 
> [   10.437488] ACPI: Early table checksum verification disabled
> [   10.439345] ACPI: RSDP 0x000000004005F955 000024 (v02 BOCHS )
> [   10.441033] ACPI: RSDT 0x000000004005F979 000034 (v01 BOCHS  BXPCRSDT 
> 00000001 BXPC 00000001)
> [   10.444045] ACPI: APIC 0x0000000040060F76 00008A (v01 BOCHS  BXPCAPIC 
> 00000001 BXPC 00000001)
> [   10.445984] ACPI: FACP 0x000000004005FA65 000074 (v01 BOCHS  BXPCFACP 
> 00000001 BXPC 00000001)
> [   10.447170] ACPI BIOS Warning (bug): Incorrect checksum in table [FACP] - 
> 0x67, should be 0x30 (20220331/tbprint-174)
> [   10.449522] ACPI: DSDT 0x000000004005FB19 00145D (v01 BOCHS  BXPCDSDT 
> 00000001 BXPC 00000001)
> [   10.451258] ACPI: FACS 0x000000004005FAD9 000040
> [   10.452245] ACPI: Reserving APIC table memory at [mem 
> 0x40060f76-0x40060fff]
> [   10.452389] ACPI: Reserving FACP table memory at [mem 
> 0x4005fa65-0x4005fad8]
> [   10.452497] ACPI: Reserving DSDT table memory at [mem 
> 0x4005fb19-0x40060f75]
> [   10.452602] ACPI: Reserving FACS table memory at [mem 
> 0x4005fad9-0x4005fb18]
> 
> 
> And these are the logs of the same boot (unsuccessful) without this
> patch:
> 
> [   10.516015] ACPI: Early table checksum verification disabled
> [   10.517732] ACPI: RSDP 0x0000000040060F1E 000024 (v02 BOCHS )
> [   10.519535] ACPI: RSDT 0x0000000040060F42 000034 (v01 BOCHS  BXPCRSDT 
> 00000001 BXPC 00000001)
> [   10.522523] ACPI: APIC 0x0000000040060F76 00008A (v01 BOCHS  BXPCAPIC 
> 00000001 BXPC 00000001)
> [   10.527453] ACPI: ���� 0x000000007FFE149D FFFFFFFF (v255 ������ �������� 
> FFFFFFFF ���� FFFFFFFF)
> [   10.528362] ACPI: Reserving APIC table memory at [mem 
> 0x40060f76-0x40060fff]
> [   10.528491] ACPI: Reserving ���� table memory at [mem 
> 0x7ffe149d-0x17ffe149b]
> 
> It is clearly a memory corruption around FACS 

Sorry I meant FACP/FADT