Re: [Xen-devel] [PATCH 05/10] xen/arm: vpl011: Allocate a new PFN in the toolstack for the virtual console

[Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>]

Hi Wei,


>>  /* --- pluggable kernel loader ------------------------------------- */
>> diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
>> index a7e839e..157381e 100644
>> --- a/tools/libxc/xc_dom_arm.c
>> +++ b/tools/libxc/xc_dom_arm.c
>> @@ -26,10 +26,11 @@
>>  #include "xg_private.h"
>>  #include "xc_dom.h"
>>
>> -#define NR_MAGIC_PAGES 3
>> +#define NR_MAGIC_PAGES 4
>>  #define CONSOLE_PFN_OFFSET 0
>>  #define XENSTORE_PFN_OFFSET 1
>>  #define MEMACCESS_PFN_OFFSET 2
>> +#define VCONSOLE_PFN_OFFSET 3
>>
>>  #define LPAE_SHIFT 9
>>
>> @@ -85,6 +86,7 @@ static int alloc_magic_pages(struct xc_dom_image *dom)
>>
>>      dom->console_pfn = base + CONSOLE_PFN_OFFSET;
>>      dom->xenstore_pfn = base + XENSTORE_PFN_OFFSET;
>> +    dom->vconsole_pfn = base + VCONSOLE_PFN_OFFSET;
>>
>>      xc_clear_domain_page(dom->xch, dom->guest_domid, dom->console_pfn);
>>      xc_clear_domain_page(dom->xch, dom->guest_domid, dom->xenstore_pfn);
>> @@ -95,6 +97,9 @@ static int alloc_magic_pages(struct xc_dom_image *dom)
>>              dom->xenstore_pfn);
>>      xc_hvm_param_set(dom->xch, dom->guest_domid, HVM_PARAM_MONITOR_RING_PFN,
>>              base + MEMACCESS_PFN_OFFSET);
>> +    xc_hvm_param_set(dom->xch, dom->guest_domid, HVM_PARAM_VCONSOLE_PFN,
>> +                     base + VCONSOLE_PFN_OFFSET);
>> +
>
> Here is something I don't quite understand (sorry I haven't been
> following the conversation closely): if pl011 is emulated, why would the
> guest need to know its PFN?

This PFN is used by Xen to setup a ring-buffer between xenconsole and itself.
Xen reads/writes data from/to this ring buffer when it gets a mmio
read/write request from the guest.

Here using the hvm call, we are passing the PFN to Xen so that it can
setup the ring buffers.

Regards,
Bhupinder

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