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

[Wei Liu <wei.liu2@citrix.com>]

On Thu, Apr 13, 2017 at 02:07:54PM +0530, Bhupinder Thakur wrote:
> 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.
> 

What I was getting at was "does the *guest* need to know the PFN"?  The
hypervisor and xenconsole daemon / client aren't the guest. Does the
guest need to know the exact PFN in order to setup MMIO?

Ultimately this is going to be decided by ARM maintainers. I'm just
curious about why it is done like this.

Wei.

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