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Re: [PATCH v3] xen/x86/pvh: handle ACPI RSDT table in PVH Dom0 build
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 25 Apr 2024 09:26:59 +0200
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- Cc: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 25 Apr 2024 07:27:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 25.04.2024 09:10, Roger Pau Monné wrote:
> On Thu, Apr 25, 2024 at 08:12:09AM +0200, Jan Beulich wrote:
>> On 24.04.2024 21:18, Daniel P. Smith wrote:
>>> @@ -1089,6 +1098,9 @@ static int __init pvh_setup_acpi_xsdt(struct domain
>>> *d, paddr_t madt_addr,
>>> xsdt->header = *table;
>>> acpi_os_unmap_memory(table, sizeof(*table));
>>>
>>> + /* In case the header is an RSDT copy, blindly ensure it has an XSDT
>>> sig */
>>> + xsdt->header.signature[0] = 'X';
>>
>> This is in no way "blindly". The size of the table elements being different
>> between RSDT and XSDT makes it mandatory to have the correct signature. Else
>> the consumer of the struct is going to be misled.
>
> The "blindly" IMO refers to the fact that the table might already have
> the right signature, but this is not checked, IOW we could do:
>
> if ( xsdt->header.signature[0] == 'R' )
> xsdt->header.signature[0] = 'X';
Right, and indeed I was seeing this as a possible further interpretation.
Yet given multiple ways of reading this, I'm of the opinion that it wants
adjusting. ", ... unconditionally ensure it has ... " may already do.
Simply dropping "blindly" would too be okay with me.
Jan
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