Re: [PATCH v2 2/3] x86: detect PIC aliasing on ports other than 0x[2A][01]

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2023-12-18 15:48, Jan Beulich wrote:
> ... in order to also deny Dom0 access through the alias ports. Without
> this it is only giving the impression of denying access to both PICs.
> Unlike for CMOS/RTC, do detection very early, to avoid disturbing 
> normal
> operation later on.
>
> Like for CMOS/RTC a fundamental assumption of the probing is that reads
> from the probed alias port won't have side effects in case it does not
> alias the respective PIC's one.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Use new command line option. s/pic/8252A/. Re-base over new earlier
>     patch. Use ISOLATE_LSB().
Hi,

coming back to this patch, which I believe didn't receive much feedback 
and thus wasn't committed, for a reason:
> --- a/xen/arch/x86/i8259.c
> +++ b/xen/arch/x86/i8259.c
> @@ -19,6 +19,7 @@
>  #include <xen/delay.h>
>  #include <asm/apic.h>
>  #include <asm/asm_defns.h>
> +#include <asm/setup.h>
Here asm/setup is included, which provides the declaration for init_IRQ, 
defined below in the file
>  void __init init_IRQ(void)
> @@ -343,6 +396,8 @@ void __init init_IRQ(void)
which is defined here. This patch would, among other things, address a 
MISRA C Rule 8.4 violation ("A compatible declaration shall be visible 
when an object or function with external linkage is defined"). I did 
send a patch concerned only with the MISRA violation, but correctly it 
was pointed out that this one was doing that and more. Perhaps someone 
can have a look at this?
>      init_8259A(0);
>
> +    probe_8259A_alias();
> +
>      for (irq = 0; platform_legacy_irq(irq); irq++) {
>          struct irq_desc *desc = irq_to_desc(irq);
>
> --- a/xen/arch/x86/include/asm/setup.h
> +++ b/xen/arch/x86/include/asm/setup.h
> @@ -46,6 +46,8 @@ extern uint8_t kbd_shift_flags;
>  extern unsigned long highmem_start;
>  #endif
>
> +extern unsigned int i8259A_alias_mask;
> +
>  extern int8_t opt_smt;
>  extern int8_t opt_probe_port_aliases;
--
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)