Re: [Xen-devel] start of day, special pages

[Daniel Kiper <dkiper@xxxxxxxxxxxx>]

On Wed, Oct 30, 2013 at 02:11:51PM +0100, Vladimir '??-coder/phcoder' 
Serbinenko wrote:
> On 30.10.2013 14:03, Konrad Rzeszutek Wilk wrote:
> > On Wed, Oct 30, 2013 at 01:32:30PM +0100, Vladimir '??-coder/phcoder' 
> > Serbinenko wrote:
> >> Hello, all. I'm writing pvgrub2 ( for those interested
> >> http://git.savannah.gnu.org/cgit/grub.git/log/?h=phcoder/newports/xen )
> >> Now I'm able to load pvgrub2 from pvgrub2. Now I'm trying to load
> >> NetBSD. Apparently NetBSD assumes that console interface is mapping in
> >> start-of-day layout and I paid special care not to map any special pages
> >> in start-of-day. Which special pages have to be mapped and where?
> >> Accoring to xen.h:
> >>  *  1. The domain is started within contiguous virtual-memory region.
> >>  *  2. The contiguous region ends on an aligned 4MB boundary.
> >>  *  3. This the order of bootstrap elements in the initial virtual region:
> >>  *      a. relocated kernel image
> >>  *      b. initial ram disk              [mod_start, mod_len]
> >>  *      c. list of allocated page frames [mfn_list, nr_pages]
> >>  *         (unless relocated due to XEN_ELFNOTE_INIT_P2M)
> >>  *      d. start_info_t structure        [register ESI (x86)]
> >
> > That structure has the information:
> >
> >
> > #ifdef XEN_HAVE_PV_GUEST_ENTRY
> > struct start_info {
> >     /* THE FOLLOWING ARE FILLED IN BOTH ON INITIAL BOOT AND ON RESUME.    */
> >     char magic[32];             /* "xen-<version>-<platform>".            */
> >     unsigned long nr_pages;     /* Total pages allocated to this domain.  */
> >     unsigned long shared_info;  /* MACHINE address of shared info struct. */
> >     uint32_t flags;             /* SIF_xxx flags.                         */
> >     xen_pfn_t store_mfn;        /* MACHINE page number of shared page.    */
> >     uint32_t store_evtchn;      /* Event channel for store communication. */
> >     union {
> >         struct {
> >             xen_pfn_t mfn;      /* MACHINE page number of console page.   
> > */  <====
> >             uint32_t  evtchn;   /* Event channel for console page.        */
> >         } domU;
> >         struct {
> >             uint32_t info_off;  /* Offset of console_info struct.         */
> >             uint32_t info_size; /* Size of console_info struct from start.*/
> >         } dom0;
> >     } console;
> >     /* THE FOLLOWING ARE ONLY FILLED IN ON INITIAL BOOT (NOT RESUME).     */
> >     unsigned long pt_base;      /* VIRTUAL address of page directory.     */
> >     unsigned long nr_pt_frames; /* Number of bootstrap p.t. frames.       */
> >     unsigned long mfn_list;     /* VIRTUAL address of page-frame list.    */
> >     unsigned long mod_start;    /* VIRTUAL address of pre-loaded module   */
> >                                 /* (PFN of pre-loaded module if           */
> >                                 /*  SIF_MOD_START_PFN set in flags).      */
> >     unsigned long mod_len;      /* Size (bytes) of pre-loaded module.     */
> > #define MAX_GUEST_CMDLINE 1024
> >     int8_t cmd_line[MAX_GUEST_CMDLINE];
> >     /* The pfn range here covers both page table and p->m table frames.   */
> >     unsigned long first_p2m_pfn;/* 1st pfn forming initial P->M table.    */
> >     unsigned long nr_p2m_frames;/* # of pfns forming initial P->M table.  */
> > };
> >
> > You need to consult console.domU.mfn.
> >
> Yes, I understand that but it's not my question. My question is where I
> should map it to when handing off control to another kernel.

I have not seen any real docs about that but IIRC pvgrub maps console
and xenstore just immediately after start info. Please look for:

...
/* Move current console, xenstore and boot MFNs to the allocated * place */
do_exchange(dom, dom->console_pfn, start_info.console.domU.mfn);
do_exchange(dom, dom->xenstore_pfn, start_info.store_mfn);
...

in xen/stubdom/grub/kexec.c file. In general this file shows how to
build properly all boot stuff. You could also check my PV kexec
implementation:

http://lists.xenproject.org/archives/html/xen-devel/2013-07/msg02613.html

Especially check kexec-tools-2.0.3_20120522.patch patch. Most interesting
stuff for you is in kexec-tools-2.0.3/kexec/arch/i386/kexec-xen-pv.c
file. It is xen-pv loader. xen_pv_load() will show you general overview.
Do not worry too much about xenstore and console pages order. It is my
arbitrary choice but I needed that in my PV kexec implementation.

You will find also there some info how to use early console (check
kexec-tools-2.0.3/purgatory/arch/i386/console-x86.c file for more
details).

If you need more info drop me a line.

Daniel

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel