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Re: [Xen-devel] [RFC PATCH] x86: Add a new physdev_op PHYSDEVOP_nr_irqs_gsi
>>> On 10.04.12 at 17:50, Lin Ming <mlin@xxxxxxxxxxxxx> wrote:
> On Tue, 2012-04-10 at 16:33 +0100, Jan Beulich wrote:
>> >>> On 10.04.12 at 17:13, Lin Ming <mlin@xxxxxxxxxxxxx> wrote:
>> > This new physdev_op is added for Linux guest kernel to get the correct
>> > nr_irqs_gsi value.
>> I'm not convinced this is really needed - the kernel can work out the
>> right number without any hypercall afaict.
> In Linux kernel:
> entries = io_apic_get_redir_entries(idx);
> gsi_cfg = mp_ioapic_gsi_routing(idx);
> gsi_cfg->gsi_base = gsi_base;
> gsi_cfg->gsi_end = gsi_base + entries - 1;
> * The number of IO-APIC IRQ registers (== #pins):
> ioapics[idx].nr_registers = entries;
> if (gsi_cfg->gsi_end >= gsi_top)
> gsi_top = gsi_cfg->gsi_end + 1;
> io_apic_get_redir_entries calls io_apic_read(), which returns wrong
> value(0xFFFFFFFF) on Xen Dom0 kernel.
I understand all of the above.
> How can we get the correct gsi_top value, which is used to set
> nr_irqs_gsi, without hypercall?
> The problem here is we don't have a Xen version of io_apic_read in Linux
Meaning you need to craft one if you need one, the more that
struct io_apic_ops already exists. The traditional kernel was able
to do so quite fine, and hence didn't need any hypercall.
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