As a further followup to the question about Xen/ia64 hypercalls,
I have now implemented and tested (but not yet checked in to the
main tree) support for access to domain memory, and have tested
it with some hypercalls that returns statistics about privop emulation.
The following (user mode!) program demonstrates the usage.
Dan
================
// test program for Xen/ia64 hypercalls that get/zero privop counts
// NOTE: break value and hypercall numbers are likely to change
// usage: to print out current privop counts
// ./privcnt
// usage: to zero out current privop counts
// ./privcnt 0
#define BUFSIZ 8192 // must be >= 8192
#define BREAKIMM 0x1000
#define GET_PRIVOP_CNT_HYPERCALL 0xffff
#define ZERO_PRIVOP_CNT_HYPERCALL 0xfffe
long get_privop_counts(char *s, long n)
{
register long r32 asm("in0") = (unsigned long)s;
register long r33 asm("in1") = n;
register long r8 asm("r8");
asm volatile("mov r2=%0; break %1;"
:: "i" (GET_PRIVOP_CNT_HYPERCALL), "i" (BREAKIMM)
: "r2", "r8", "memory");
return r8;
}
long zero_privop_counts(char *s, long n)
{
register long r32 asm("in0") = (unsigned long)s;
register long r33 asm("in1") = n;
register long r8 asm("r8");
asm volatile("mov r2=%0; break %1;"
:: "i" (ZERO_PRIVOP_CNT_HYPERCALL), "i" (BREAKIMM)
: "r2", "r8", "memory");
return r8;
}
main(int ac, char **av)
{
char buf[BUFSIZ];
if (ac > 1) {
// zero privop counts
if ((long)zero_privop_counts(buf,BUFSIZ) == -1)
printf("privcnt: failed\n");
else printf(buf);
}
else {
// get privop counts
if ((long)get_privop_counts(buf,BUFSIZ) == -1)
printf("privcnt: failed\n");
else printf(buf);
}
}
> -----Original Message-----
> From: Magenheimer, Dan (HP Labs Fort Collins)
> Sent: Friday, February 18, 2005 12:13 PM
> To: 'Håvard Bjerke'
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: RE: Xen/ia64
>
> There is an implementation of Xen/ia64 hypercalls already.
> See:
>
> http://article.gmane.org/gmane.comp.emulators.xen.devel/4734
>
> This isn't cast in concrete... if there is a better way,
> we can change it. But let me clarify what is there:
>
> - There is a default break value that Xen/ia64 interprets as
> a hypercall. This is a per-domain variable so if a future
> version of Linux uses this break value to do something else,
> it can be changed (e.g. as a domain launch parameter).
> - If the break value does not match, the break is reflected
> to the executing domain. If it does match, r2 contains the
> hypercall number.
> - The only implemented hypercalls now are for firmware
> (EFI/SAL/PAL) emulation. These are really "hyperthunks"
> since domain loading generates stubs that contain the break
> instructions.
> - The parameter interface is dependent on the hypercall number.
> E.g. PAL hypercalls pass parameters in different registers
> than SAL hypercalls. Most Xen/x86 calls pass parameters in
> memory. It would be nice if Xen/ia64 could take advantage
> of the register stack to pass all parameters in registers
> but if this messes up portability (e.g. for frontend/backend
> driver code) between Xen/x86 and Xen/ia64, it's probably
> not worth it.
> - Right now, there is very limited support for Xen/ia64 to
> access domain memory (it's only used for fetching opcodes
> for privop emulation). I have a patch that fixes this but
> there's a bug that I haven't tracked down yet so I haven't
> promoted it to -unstable. Once this code is there, we can
> try out hypercalls that pass parameters via domain memory.
> (The patch also implements two test hypercalls to fetch
> and zero-out privop counters and pass back a long text
> string to domain0.)
>
> Linux/ia64 implements something called "fsyscall" (fast
> system call) for certain system calls, which uses the "epc"
> instruction instead of break. There are many restrictions to
> fsyscalls, but they may work for Xen/ia64 for certain simple
> hypercalls. But since that is strictly a performance improvement,
> let's try to stick to break instructions for hypercalls at
> first.
>
> Dan
>
> P.S. I will be unable to access email soon until March 1.
>
> > -----Original Message-----
> > From: Håvard Bjerke [mailto:Havard.Bjerke@xxxxxxxxxxx]
> > Sent: Friday, February 18, 2005 3:15 AM
> > To: Magenheimer, Dan (HP Labs Fort Collins)
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxxx
> > Subject: Xen/ia64
> >
> > Has anyone made any thoughts as to how hypercalls should be
> > implemented in Xen/ia64?
> >
> > In Xen/x86 they are basically syscalls, only with interrupt
> > vector 0x82 instead of 0x80. So it's a matter of pushing the
> > registers into the stack, loading the hypercall number (long)
> > and arguments (5x long) into the registers, and interrupting
> > with 'int 0x82':
> > __asm__ __volatile__ (
> > "pushl %%ebx; pushl %%ecx; pushl %%edx; pushl
> > %%esi; pushl %%edi; "
> > "movl 4(%%eax),%%ebx ;"
> > "movl 8(%%eax),%%ecx ;"
> > "movl 12(%%eax),%%edx ;"
> > "movl 16(%%eax),%%esi ;"
> > "movl 20(%%eax),%%edi ;"
> > "movl (%%eax),%%eax ;"
> > TRAP_INSTR "; " // = int 0x82
> > "popl %%edi; popl %%esi; popl %%edx; popl %%ecx;
> > popl %%ebx"
> > : "=a" (ret) : "0" (&hypercall) : "memory" );
> >
> > However, in Linux/ia64 a syscall is called with a break instruction:
> > mov r15 = NR // the syscall number. r15 is a scratch register.
> > break 0x100000
> > [...]
> >
> > What's the ideal way to do a hypercall in Xen/ia64? Simply
> > use 'break 0x100001'? Or is 0x100001 reserved for something
> > else in Linux/ia64?
> >
> > Håvard
> >
> > --
> > Håvard K. F. Bjerke
> > http://www.idi.ntnu.no/~havarbj/
> >
>
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