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lguest: documentation V: Host

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Documentation: The Host

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rusty Russell 2007-07-26 10:41:04 -07:00 • committed by Linus Torvalds
parent dde797899a
commit bff672e630
6 changed files with 924 additions and 85 deletions
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118
drivers/lguest/hypercalls.c
View file

@ -28,37 +28,63 @@
#include <irq_vectors.h>
#include "lg.h"
/*H:120 This is the core hypercall routine: where the Guest gets what it
* wants. Or gets killed. Or, in the case of LHCALL_CRASH, both.
*
* Remember from the Guest: %eax == which call to make, and the arguments are
* packed into %edx, %ebx and %ecx if needed. */
static void do_hcall(struct lguest *lg, struct lguest_regs *regs)
{
switch (regs->eax) {
case LHCALL_FLUSH_ASYNC:
/* This call does nothing, except by breaking out of the Guest
* it makes us process all the asynchronous hypercalls. */
break;
case LHCALL_LGUEST_INIT:
/* You can't get here unless you're already initialized. Don't
* do that. */
kill_guest(lg, "already have lguest_data");
break;
case LHCALL_CRASH: {
/* Crash is such a trivial hypercall that we do it in four
* lines right here. */
char msg[128];
/* If the lgread fails, it will call kill_guest() itself; the
* kill_guest() with the message will be ignored. */
lgread(lg, msg, regs->edx, sizeof(msg));
msg[sizeof(msg)-1] = '\0';
kill_guest(lg, "CRASH: %s", msg);
break;
}
case LHCALL_FLUSH_TLB:
/* FLUSH_TLB comes in two flavors, depending on the
* argument: */
if (regs->edx)
guest_pagetable_clear_all(lg);
else
guest_pagetable_flush_user(lg);
break;
case LHCALL_GET_WALLCLOCK: {
/* The Guest wants to know the real time in seconds since 1970,
* in good Unix tradition. */
struct timespec ts;
ktime_get_real_ts(&ts);
regs->eax = ts.tv_sec;
break;
}
case LHCALL_BIND_DMA:
/* BIND_DMA really wants four arguments, but it's the only call
* which does. So the Guest packs the number of buffers and
* the interrupt number into the final argument, and we decode
* it here. This can legitimately fail, since we currently
* place a limit on the number of DMA pools a Guest can have.
* So we return true or false from this call. */
regs->eax = bind_dma(lg, regs->edx, regs->ebx,
regs->ecx >> 8, regs->ecx & 0xFF);
break;
/* All these calls simply pass the arguments through to the right
* routines. */
case LHCALL_SEND_DMA:
send_dma(lg, regs->edx, regs->ebx);
break;
@ -86,10 +112,13 @@ static void do_hcall(struct lguest *lg, struct lguest_regs *regs)
case LHCALL_SET_CLOCKEVENT:
guest_set_clockevent(lg, regs->edx);
break;
case LHCALL_TS:
/* This sets the TS flag, as we saw used in run_guest(). */
lg->ts = regs->edx;
break;
case LHCALL_HALT:
/* Similarly, this sets the halted flag for run_guest(). */
lg->halted = 1;
break;
default:
@ -97,25 +126,42 @@ static void do_hcall(struct lguest *lg, struct lguest_regs *regs)
}
}
/* We always do queued calls before actual hypercall. */
/* Asynchronous hypercalls are easy: we just look in the array in the Guest's
* "struct lguest_data" and see if there are any new ones marked "ready".
*
* We are careful to do these in order: obviously we respect the order the
* Guest put them in the ring, but we also promise the Guest that they will
* happen before any normal hypercall (which is why we check this before
* checking for a normal hcall). */
static void do_async_hcalls(struct lguest *lg)
{
unsigned int i;
u8 st[LHCALL_RING_SIZE];
/* For simplicity, we copy the entire call status array in at once. */
if (copy_from_user(&st, &lg->lguest_data->hcall_status, sizeof(st)))
return;
/* We process "struct lguest_data"s hcalls[] ring once. */
for (i = 0; i < ARRAY_SIZE(st); i++) {
struct lguest_regs regs;
/* We remember where we were up to from last time. This makes
* sure that the hypercalls are done in the order the Guest
* places them in the ring. */
unsigned int n = lg->next_hcall;
/* 0xFF means there's no call here (yet). */
if (st[n] == 0xFF)
break;
/* OK, we have hypercall. Increment the "next_hcall" cursor,
* and wrap back to 0 if we reach the end. */
if (++lg->next_hcall == LHCALL_RING_SIZE)
lg->next_hcall = 0;
/* We copy the hypercall arguments into a fake register
* structure. This makes life simple for do_hcall(). */
if (get_user(regs.eax, &lg->lguest_data->hcalls[n].eax)
|| get_user(regs.edx, &lg->lguest_data->hcalls[n].edx)
|| get_user(regs.ecx, &lg->lguest_data->hcalls[n].ecx)
@ -124,74 +170,126 @@ static void do_async_hcalls(struct lguest *lg)
break;
}
/* Do the hypercall, same as a normal one. */
do_hcall(lg, &regs);
/* Mark the hypercall done. */
if (put_user(0xFF, &lg->lguest_data->hcall_status[n])) {
kill_guest(lg, "Writing result for async hypercall");
break;
}
/* Stop doing hypercalls if we've just done a DMA to the
* Launcher: it needs to service this first. */
if (lg->dma_is_pending)
break;
}
}
/* Last of all, we look at what happens first of all. The very first time the
* Guest makes a hypercall, we end up here to set things up: */
static void initialize(struct lguest *lg)
{
u32 tsc_speed;
/* You can't do anything until you're initialized. The Guest knows the
* rules, so we're unforgiving here. */
if (lg->regs->eax != LHCALL_LGUEST_INIT) {
kill_guest(lg, "hypercall %li before LGUEST_INIT",
lg->regs->eax);
return;
}
/* We only tell the guest to use the TSC if it's reliable. */
/* We insist that the Time Stamp Counter exist and doesn't change with
* cpu frequency. Some devious chip manufacturers decided that TSC
* changes could be handled in software. I decided that time going
* backwards might be good for benchmarks, but it's bad for users.
*
* We also insist that the TSC be stable: the kernel detects unreliable
* TSCs for its own purposes, and we use that here. */
if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && !check_tsc_unstable())
tsc_speed = tsc_khz;
else
tsc_speed = 0;
/* The pointer to the Guest's "struct lguest_data" is the only
* argument. */
lg->lguest_data = (struct lguest_data __user *)lg->regs->edx;
/* We check here so we can simply copy_to_user/from_user */
/* If we check the address they gave is OK now, we can simply
* copy_to_user/from_user from now on rather than using lgread/lgwrite.
* I put this in to show that I'm not immune to writing stupid
* optimizations. */
if (!lguest_address_ok(lg, lg->regs->edx, sizeof(*lg->lguest_data))) {
kill_guest(lg, "bad guest page %p", lg->lguest_data);
return;
}
/* The Guest tells us where we're not to deliver interrupts by putting
* the range of addresses into "struct lguest_data". */
if (get_user(lg->noirq_start, &lg->lguest_data->noirq_start)
|| get_user(lg->noirq_end, &lg->lguest_data->noirq_end)
/* We reserve the top pgd entry. */
/* We tell the Guest that it can't use the top 4MB of virtual
* addresses used by the Switcher. */
|| put_user(4U*1024*1024, &lg->lguest_data->reserve_mem)
|| put_user(tsc_speed, &lg->lguest_data->tsc_khz)
/* We also give the Guest a unique id, as used in lguest_net.c. */
|| put_user(lg->guestid, &lg->lguest_data->guestid))
kill_guest(lg, "bad guest page %p", lg->lguest_data);
/* This is the one case where the above accesses might have
* been the first write to a Guest page. This may have caused
* a copy-on-write fault, but the Guest might be referring to
* the old (read-only) page. */
/* This is the one case where the above accesses might have been the
* first write to a Guest page. This may have caused a copy-on-write
* fault, but the Guest might be referring to the old (read-only)
* page. */
guest_pagetable_clear_all(lg);
}
/* Now we've examined the hypercall code; our Guest can make requests. There
* is one other way we can do things for the Guest, as we see in
* emulate_insn(). */
/* Even if we go out to userspace and come back, we don't want to do
* the hypercall again. */
/*H:110 Tricky point: we mark the hypercall as "done" once we've done it.
* Normally we don't need to do this: the Guest will run again and update the
* trap number before we come back around the run_guest() loop to
* do_hypercalls().
*
* However, if we are signalled or the Guest sends DMA to the Launcher, that
* loop will exit without running the Guest. When it comes back it would try
* to re-run the hypercall. */
static void clear_hcall(struct lguest *lg)
{
lg->regs->trapnum = 255;
}
/*H:100
* Hypercalls
*
* Remember from the Guest, hypercalls come in two flavors: normal and
* asynchronous. This file handles both of types.
*/
void do_hypercalls(struct lguest *lg)
{
/* Not initialized yet? */
if (unlikely(!lg->lguest_data)) {
/* Did the Guest make a hypercall? We might have come back for
* some other reason (an interrupt, a different trap). */
if (lg->regs->trapnum == LGUEST_TRAP_ENTRY) {
/* Set up the "struct lguest_data" */
initialize(lg);
/* The hypercall is done. */
clear_hcall(lg);
}
return;
}
/* The Guest has initialized.
*
* Look in the hypercall ring for the async hypercalls: */
do_async_hcalls(lg);
/* If we stopped reading the hypercall ring because the Guest did a
* SEND_DMA to the Launcher, we want to return now. Otherwise if the
* Guest asked us to do a hypercall, we do it. */
if (!lg->dma_is_pending && lg->regs->trapnum == LGUEST_TRAP_ENTRY) {
do_hcall(lg, lg->regs);
/* The hypercall is done. */
clear_hcall(lg);
}
}