Re: [PATCH v4 10/19] xen: setup hypercall page for PVH

[Daniel Kiper]

On Fri, Nov 02, 2018 at 01:37:29PM +0100, Juergen Gross wrote:
> Add the needed code to setup the hypercall page for calling into the
> Xen hypervisor.
>
> Signed-off-by: Juergen Gross <address@hidden>
> ---
> V3: grub_xen_early_halt->grub_xen_panic (Roger Pau Monné)
>     issue panic message (Roger Pau Monné)
>     rewrite grub_xen_hypercall to avoid register variables (Daniel Kiper)
> ---
>  grub-core/kern/i386/xen/pvh.c | 69 
> +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 69 insertions(+)
>
> diff --git a/grub-core/kern/i386/xen/pvh.c b/grub-core/kern/i386/xen/pvh.c
> index ac6181f4e..7e90a4538 100644
> --- a/grub-core/kern/i386/xen/pvh.c
> +++ b/grub-core/kern/i386/xen/pvh.c
> @@ -20,14 +20,83 @@
>  #include <grub/misc.h>
>  #include <grub/memory.h>
>  #include <grub/mm.h>
> +#include <grub/i386/cpuid.h>
> +#include <grub/i386/io.h>
>  #include <grub/xen.h>
>  #include <grub/machine/kernel.h>
>
> +#define XEN_CONSOLE_PORT   0xe9

I think that this is not PVH specific thing. Could you move this to
more generic Xen header?

>  grub_uint64_t grub_rsdp_addr;

Hmmm... It seems to me that immediately after patch #8 GRUB2 build is
broken. Is not it?

> +static char hypercall_page[GRUB_XEN_PAGE_SIZE]
> +  __attribute__ ((aligned (GRUB_XEN_PAGE_SIZE)));
> +
> +static grub_uint32_t xen_cpuid_base;
> +
> +static void
> +grub_xen_panic (const char *msg)
> +{
> +  const char *c;
> +
> +  for (c = msg; *c; c++)
> +    grub_outb (*c, XEN_CONSOLE_PORT);
> +
> +  asm volatile ("hlt");

Should not you do something similar to grub-core/lib/i386/halt.c:stop() here?

> +}
> +
> +static void
> +grub_xen_cpuid_base (void)
> +{
> +  grub_uint32_t base, eax, signature[3];
> +
> +  for (base = 0x40000000; base < 0x40010000; base += 0x100)
> +    {
> +      grub_cpuid (base, eax, signature[0], signature[1], signature[2]);
> +      if (!grub_memcmp ("XenVMMXenVMM", signature, 12) && (eax - base) >= 2)
> +     {
> +       xen_cpuid_base = base;
> +       return;
> +     }
> +    }
> +
> +  grub_xen_panic ("Found no Xen signature.\n");

"Found no Xen signature!\nSystem halted!\n"

Or maybe grub_xen_panic() should always add "System halted!\n".

> +}
> +
> +static void
> +grub_xen_setup_hypercall_page (void)
> +{
> +  grub_uint32_t msr, pfn, eax, ebx, ecx, edx;
> +
> +  grub_cpuid (xen_cpuid_base + 2, eax, ebx, ecx, edx);
> +  msr = ebx;
> +  pfn = (grub_uint32_t) (&hypercall_page[0]);

Could not you use hypercall_page alone here?

> +
> +  asm volatile ("wrmsr" : : "c" (msr), "a" (pfn), "d" (0) : "memory");
> +}
> +
> +int
> +grub_xen_hypercall (grub_uint32_t callno, grub_uint32_t a0,
> +                 grub_uint32_t a1, grub_uint32_t a2,
> +                 grub_uint32_t a3, grub_uint32_t a4,
> +                 grub_uint32_t a5 __attribute__ ((unused)))
> +{
> +  grub_uint32_t __res, __ign0, __ign1, __ign2, __ign3, __ign4;
> +
> +  asm volatile ("call *%[callno]"
> +             : "=a" (__res), "=b" (__ign0), "=c" (__ign1), "=d" (__ign2),
> +               "=S" (__ign3), "=D" (__ign4)
> +             : "1" (a0), "2" (a1), "3" (a2), "4" (a3), "5" (a4),

I think that you can drop all __ign* variables if you specify proper
registers in input argument. If this does not work you can use "+"
modifier instead of "=" in the output argument.

> +               [callno] "a" (&hypercall_page[callno * 32])
> +             : "memory");
> +  return __res;
> +}

Daniel