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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan