Re: [PATCH 1/2] xen/x86/pvh: use preset XSDT header for XSDT generation

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, May 16, 2023 at 11:13:17AM +0200, Jan Beulich wrote:
> On 16.05.2023 10:24, Roger Pau Monné wrote:
> > On Tue, May 16, 2023 at 10:10:07AM +0200, Roger Pau Monné wrote:
> >> On Mon, May 15, 2023 at 05:16:27PM -0700, Stefano Stabellini wrote:
> >>> On Mon, 15 May 2023, Jan Beulich wrote:
> >>>> On 15.05.2023 10:48, Roger Pau Monné wrote:
> >>>>> On Fri, May 12, 2023 at 06:17:19PM -0700, Stefano Stabellini wrote:
> >>>>>> From: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> >>>>>>
> >>>>>> Xen always generates a XSDT table even if the firmware provided a RSDT
> >>>>>> table. Instead of copying the XSDT header from the firmware table (that
> >>>>>> might be missing), generate the XSDT header from a preset.
> >>>>>>
> >>>>>> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> >>>>>> ---
> >>>>>>  xen/arch/x86/hvm/dom0_build.c | 32 +++++++++-----------------------
> >>>>>>  1 file changed, 9 insertions(+), 23 deletions(-)
> >>>>>>
> >>>>>> diff --git a/xen/arch/x86/hvm/dom0_build.c 
> >>>>>> b/xen/arch/x86/hvm/dom0_build.c
> >>>>>> index 307edc6a8c..5fde769863 100644
> >>>>>> --- a/xen/arch/x86/hvm/dom0_build.c
> >>>>>> +++ b/xen/arch/x86/hvm/dom0_build.c
> >>>>>> @@ -963,13 +963,18 @@ static int __init pvh_setup_acpi_xsdt(struct 
> >>>>>> domain *d, paddr_t madt_addr,
> >>>>>>                                        paddr_t *addr)
> >>>>>>  {
> >>>>>>      struct acpi_table_xsdt *xsdt;
> >>>>>> -    struct acpi_table_header *table;
> >>>>>> -    struct acpi_table_rsdp *rsdp;
> >>>>>>      const struct acpi_table_desc *tables = 
> >>>>>> acpi_gbl_root_table_list.tables;
> >>>>>>      unsigned long size = sizeof(*xsdt);
> >>>>>>      unsigned int i, j, num_tables = 0;
> >>>>>> -    paddr_t xsdt_paddr;
> >>>>>>      int rc;
> >>>>>> +    struct acpi_table_header header = {
> >>>>>> +        .signature    = "XSDT",
> >>>>>> +        .length       = sizeof(struct acpi_table_header),
> >>>>>> +        .revision     = 0x1,
> >>>>>> +        .oem_id       = "Xen",
> >>>>>> +        .oem_table_id = "HVM",
> >>>>>
> >>>>> I think this is wrong, as according to the spec the OEM Table ID must
> >>>>> match the OEM Table ID in the FADT.
> >>>>>
> >>>>> We likely want to copy the OEM ID and OEM Table ID from the RSDP, and
> >>>>> possibly also the other OEM related fields.
> >>>>>
> >>>>> Alternatively we might want to copy and use the RSDT on systems that
> >>>>> lack an XSDT, or even just copy the header from the RSDT into Xen's
> >>>>> crafted XSDT, since the format of the RSDP and the XSDT headers are
> >>>>> exactly the same (the difference is in the size of the description
> >>>>> headers that come after).
> >>>>
> >>>> I guess I'd prefer that last variant.
> >>>
> >>> I tried this approach (together with the second patch for necessity) and
> >>> it worked.
> >>>
> >>> diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
> >>> index fd2cbf68bc..11d6d1bc23 100644
> >>> --- a/xen/arch/x86/hvm/dom0_build.c
> >>> +++ b/xen/arch/x86/hvm/dom0_build.c
> >>> @@ -967,6 +967,10 @@ static int __init pvh_setup_acpi_xsdt(struct domain 
> >>> *d, paddr_t madt_addr,
> >>>          goto out;
> >>>      }
> >>>      xsdt_paddr = rsdp->xsdt_physical_address;
> >>> +    if ( !xsdt_paddr )
> >>> +    {
> >>> +        xsdt_paddr = rsdp->rsdt_physical_address;
> >>> +    }
> >>>      acpi_os_unmap_memory(rsdp, sizeof(*rsdp));
> >>>      table = acpi_os_map_memory(xsdt_paddr, sizeof(*table));
> >>>      if ( !table )
> >>
> >> To be slightly more consistent, could you use:
> >>
> >> /*
> >>  * Note the header is the same for both RSDT and XSDT, so it's fine to
> >>  * copy the native RSDT header to the Xen crafted XSDT if no native
> >>  * XSDT is available.
> >>  */
> >> if (rsdp->revision > 1 && rsdp->xsdt_physical_address)
> >>     sdt_paddr = rsdp->xsdt_physical_address;
> >> else
> >>     sdt_paddr = rsdp->rsdt_physical_address;
> >>
> >> It was an oversight of mine to not check for the RSDP revision, as
> >> RSDP < 2 will never have an XSDT.  Also add:
> >>
> >> Fixes: 1d74282c455f ('x86: setup PVHv2 Dom0 ACPI tables')
> > 
> > Just realized this will require some more work so that the guest
> > (dom0) provided RSDP is at least revision 2.  You will need to adjust
> > the field and recalculate the checksum if needed.
> 
> We could also mandate ACPI version >= 2 for PVH Dom0.

Sorry, mentioned on IRC, the above is not required because the RSDP
provided to dom0 is already crafted by Xen and unconditionally set to
version == 2.  There's no need to adjust the RSDP at all.

Thanks, Roger.