diff options
Diffstat (limited to 'drivers/lguest/core.c')
| -rw-r--r-- | drivers/lguest/core.c | 51 |
1 files changed, 47 insertions, 4 deletions
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c index c0f50b4dd2f1..0a46e8837d9a 100644 --- a/drivers/lguest/core.c +++ b/drivers/lguest/core.c @@ -393,46 +393,89 @@ static void set_ts(void) write_cr0(cr0|8); } +/*S:010 + * We are getting close to the Switcher. + * + * Remember that each CPU has two pages which are visible to the Guest when it + * runs on that CPU. This has to contain the state for that Guest: we copy the + * state in just before we run the Guest. + * + * Each Guest has "changed" flags which indicate what has changed in the Guest + * since it last ran. We saw this set in interrupts_and_traps.c and + * segments.c. + */ static void copy_in_guest_info(struct lguest *lg, struct lguest_pages *pages) { + /* Copying all this data can be quite expensive. We usually run the + * same Guest we ran last time (and that Guest hasn't run anywhere else + * meanwhile). If that's not the case, we pretend everything in the + * Guest has changed. */ if (__get_cpu_var(last_guest) != lg || lg->last_pages != pages) { __get_cpu_var(last_guest) = lg; lg->last_pages = pages; lg->changed = CHANGED_ALL; } - /* These are pretty cheap, so we do them unconditionally. */ + /* These copies are pretty cheap, so we do them unconditionally: */ + /* Save the current Host top-level page directory. */ pages->state.host_cr3 = __pa(current->mm->pgd); + /* Set up the Guest's page tables to see this CPU's pages (and no + * other CPU's pages). */ map_switcher_in_guest(lg, pages); + /* Set up the two "TSS" members which tell the CPU what stack to use + * for traps which do directly into the Guest (ie. traps at privilege + * level 1). */ pages->state.guest_tss.esp1 = lg->esp1; pages->state.guest_tss.ss1 = lg->ss1; - /* Copy direct trap entries. */ + /* Copy direct-to-Guest trap entries. */ if (lg->changed & CHANGED_IDT) copy_traps(lg, pages->state.guest_idt, default_idt_entries); - /* Copy all GDT entries but the TSS. */ + /* Copy all GDT entries which the Guest can change. */ if (lg->changed & CHANGED_GDT) copy_gdt(lg, pages->state.guest_gdt); /* If only the TLS entries have changed, copy them. */ else if (lg->changed & CHANGED_GDT_TLS) copy_gdt_tls(lg, pages->state.guest_gdt); + /* Mark the Guest as unchanged for next time. */ lg->changed = 0; } +/* Finally: the code to actually call into the Switcher to run the Guest. */ static void run_guest_once(struct lguest *lg, struct lguest_pages *pages) { + /* This is a dummy value we need for GCC's sake. */ unsigned int clobber; + /* Copy the guest-specific information into this CPU's "struct + * lguest_pages". */ copy_in_guest_info(lg, pages); - /* Put eflags on stack, lcall does rest: suitable for iret return. */ + /* Now: we push the "eflags" register on the stack, then do an "lcall". + * This is how we change from using the kernel code segment to using + * the dedicated lguest code segment, as well as jumping into the + * Switcher. + * + * The lcall also pushes the old code segment (KERNEL_CS) onto the + * stack, then the address of this call. This stack layout happens to + * exactly match the stack of an interrupt... */ asm volatile("pushf; lcall *lguest_entry" + /* This is how we tell GCC that %eax ("a") and %ebx ("b") + * are changed by this routine. The "=" means output. */ : "=a"(clobber), "=b"(clobber) + /* %eax contains the pages pointer. ("0" refers to the + * 0-th argument above, ie "a"). %ebx contains the + * physical address of the Guest's top-level page + * directory. */ : "0"(pages), "1"(__pa(lg->pgdirs[lg->pgdidx].pgdir)) + /* We tell gcc that all these registers could change, + * which means we don't have to save and restore them in + * the Switcher. */ : "memory", "%edx", "%ecx", "%edi", "%esi"); } +/*:*/ /*H:030 Let's jump straight to the the main loop which runs the Guest. * Remember, this is called by the Launcher reading /dev/lguest, and we keep |