diff options
Diffstat (limited to 'drivers/lguest/hypercalls.c')
| -rw-r--r-- | drivers/lguest/hypercalls.c | 127 |
1 files changed, 115 insertions, 12 deletions
diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c index ea52ca451f7..7a5299f9679 100644 --- a/drivers/lguest/hypercalls.c +++ b/drivers/lguest/hypercalls.c @@ -1,5 +1,10 @@ -/* Actual hypercalls, which allow guests to actually do something. - Copyright (C) 2006 Rusty Russell IBM Corporation +/*P:500 Just as userspace programs request kernel operations through a system + * call, the Guest requests Host operations through a "hypercall". You might + * notice this nomenclature doesn't really follow any logic, but the name has + * been around for long enough that we're stuck with it. As you'd expect, this + * code is basically a one big switch statement. :*/ + +/* Copyright (C) 2006 Rusty Russell IBM Corporation This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -23,37 +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; @@ -81,10 +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: @@ -92,25 +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) @@ -119,74 +170,126 @@ static void do_async_hcalls(struct lguest *lg) break; } + /* Do the hypercall, same as a normal one. */ do_hcall(lg, ®s); + + /* 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); } } |