Re: [PATCH] x86/ioapic: Check 1k alignment for IO-APIC physical addresses

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/11/2023 5:36 pm, Roger Pau Monné wrote:
> On Mon, Nov 20, 2023 at 03:10:06PM +0000, Andrew Cooper wrote:
>> The MP spec requires a minimum of 1k alignment.  So too does Xen's use of a
>> single fixmap page to map the IO-APIC.
>>
>> Reject out-of-spec values so we don't end up in a position where a bad
>> firmware value causes Xen to use the wrong mapping.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Wei Liu <wl@xxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> ---
>>  xen/arch/x86/io_apic.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
>> index 0ef61fb2f167..db1ea6e2f2ca 100644
>> --- a/xen/arch/x86/io_apic.c
>> +++ b/xen/arch/x86/io_apic.c
>> @@ -2589,10 +2589,11 @@ static void __init ioapic_init_mappings(void)
>>          union IO_APIC_reg_01 reg_01;
>>          paddr_t ioapic_phys = mp_ioapics[i].mpc_apicaddr;
>>  
>> -        if ( !ioapic_phys )
>> +        if ( !ioapic_phys || (ioapic_phys & (KB(1) - 1)) )
> Might be clearer to use !IS_ALIGNED()

Hmm, yeah.  Will change.

> , otherwise:
>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks.

>
>>          {
>>              printk(KERN_ERR
>> -                   "WARNING: bogus zero IO-APIC address found in MPTABLE, 
>> disabling IO/APIC support!\n");
>> +                   "WARNING: bogus IO-APIC address %08lx found in MPTABLE, 
>> disabling IO/APIC support!\n",
> FWIW, I think the '!' at the end is not useful, and I would adjust
> the last 'IO/APIC' to 'IO-APIC' if already modifying the line.

Ok.  will do.

~Andrew