Commit 4cd8b5e2 authored by Matias Zabaljauregui's avatar Matias Zabaljauregui Committed by Rusty Russell
Browse files

lguest: use KVM hypercalls



Impact: cleanup

This patch allow us to use KVM hypercalls

Signed-off-by: Matias Zabaljauregui <zabaljauregui at gmail.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent b7ff99ea
......@@ -26,36 +26,20 @@
#ifndef __ASSEMBLY__
#include <asm/hw_irq.h>
#include <asm/kvm_para.h>
/*G:031 But first, how does our Guest contact the Host to ask for privileged
* operations? There are two ways: the direct way is to make a "hypercall",
* to make requests of the Host Itself.
*
* Our hypercall mechanism uses the highest unused trap code (traps 32 and
* above are used by real hardware interrupts). Fifteen hypercalls are
* We use the KVM hypercall mechanism. Eighteen hypercalls are
* available: the hypercall number is put in the %eax register, and the
* arguments (when required) are placed in %edx, %ebx and %ecx. If a return
* arguments (when required) are placed in %ebx, %ecx and %edx. If a return
* value makes sense, it's returned in %eax.
*
* Grossly invalid calls result in Sudden Death at the hands of the vengeful
* Host, rather than returning failure. This reflects Winston Churchill's
* definition of a gentleman: "someone who is only rude intentionally". */
static inline unsigned long
hcall(unsigned long call,
unsigned long arg1, unsigned long arg2, unsigned long arg3)
{
/* "int" is the Intel instruction to trigger a trap. */
asm volatile("int $" __stringify(LGUEST_TRAP_ENTRY)
/* The call in %eax (aka "a") might be overwritten */
: "=a"(call)
/* The arguments are in %eax, %edx, %ebx & %ecx */
: "a"(call), "d"(arg1), "b"(arg2), "c"(arg3)
/* "memory" means this might write somewhere in memory.
* This isn't true for all calls, but it's safe to tell
* gcc that it might happen so it doesn't get clever. */
: "memory");
return call;
}
/*:*/
/* Can't use our min() macro here: needs to be a constant */
......@@ -64,7 +48,7 @@ hcall(unsigned long call,
#define LHCALL_RING_SIZE 64
struct hcall_args {
/* These map directly onto eax, ebx, ecx, edx in struct lguest_regs */
unsigned long arg0, arg2, arg3, arg1;
unsigned long arg0, arg1, arg2, arg3;
};
#endif /* !__ASSEMBLY__ */
......
......@@ -107,7 +107,7 @@ static void async_hcall(unsigned long call, unsigned long arg1,
local_irq_save(flags);
if (lguest_data.hcall_status[next_call] != 0xFF) {
/* Table full, so do normal hcall which will flush table. */
hcall(call, arg1, arg2, arg3);
kvm_hypercall3(call, arg1, arg2, arg3);
} else {
lguest_data.hcalls[next_call].arg0 = call;
lguest_data.hcalls[next_call].arg1 = arg1;
......@@ -134,13 +134,32 @@ static void async_hcall(unsigned long call, unsigned long arg1,
*
* So, when we're in lazy mode, we call async_hcall() to store the call for
* future processing: */
static void lazy_hcall(unsigned long call,
static void lazy_hcall1(unsigned long call,
unsigned long arg1)
{
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
kvm_hypercall1(call, arg1);
else
async_hcall(call, arg1, 0, 0);
}
static void lazy_hcall2(unsigned long call,
unsigned long arg1,
unsigned long arg2)
{
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
kvm_hypercall2(call, arg1, arg2);
else
async_hcall(call, arg1, arg2, 0);
}
static void lazy_hcall3(unsigned long call,
unsigned long arg1,
unsigned long arg2,
unsigned long arg3)
{
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
hcall(call, arg1, arg2, arg3);
kvm_hypercall3(call, arg1, arg2, arg3);
else
async_hcall(call, arg1, arg2, arg3);
}
......@@ -150,7 +169,7 @@ static void lazy_hcall(unsigned long call,
static void lguest_leave_lazy_mode(void)
{
paravirt_leave_lazy(paravirt_get_lazy_mode());
hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
kvm_hypercall0(LHCALL_FLUSH_ASYNC);
}
/*G:033
......@@ -229,7 +248,7 @@ static void lguest_write_idt_entry(gate_desc *dt,
/* Keep the local copy up to date. */
native_write_idt_entry(dt, entrynum, g);
/* Tell Host about this new entry. */
hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, desc[0], desc[1]);
kvm_hypercall3(LHCALL_LOAD_IDT_ENTRY, entrynum, desc[0], desc[1]);
}
/* Changing to a different IDT is very rare: we keep the IDT up-to-date every
......@@ -241,7 +260,7 @@ static void lguest_load_idt(const struct desc_ptr *desc)
struct desc_struct *idt = (void *)desc->address;
for (i = 0; i < (desc->size+1)/8; i++)
hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
kvm_hypercall3(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
}
/*
......@@ -261,8 +280,8 @@ static void lguest_load_idt(const struct desc_ptr *desc)
*/
static void lguest_load_gdt(const struct desc_ptr *desc)
{
BUG_ON((desc->size+1)/8 != GDT_ENTRIES);
hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0);
BUG_ON((desc->size + 1) / 8 != GDT_ENTRIES);
kvm_hypercall2(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES);
}
/* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
......@@ -272,7 +291,7 @@ static void lguest_write_gdt_entry(struct desc_struct *dt, int entrynum,
const void *desc, int type)
{
native_write_gdt_entry(dt, entrynum, desc, type);
hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0);
kvm_hypercall2(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES);
}
/* OK, I lied. There are three "thread local storage" GDT entries which change
......@@ -284,7 +303,7 @@ static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
* can't handle us removing entries we're currently using. So we clear
* the GS register here: if it's needed it'll be reloaded anyway. */
lazy_load_gs(0);
lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
lazy_hcall2(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu);
}
/*G:038 That's enough excitement for now, back to ploughing through each of
......@@ -382,7 +401,7 @@ static void lguest_cpuid(unsigned int *ax, unsigned int *bx,
static unsigned long current_cr0;
static void lguest_write_cr0(unsigned long val)
{
lazy_hcall(LHCALL_TS, val & X86_CR0_TS, 0, 0);
lazy_hcall1(LHCALL_TS, val & X86_CR0_TS);
current_cr0 = val;
}
......@@ -396,7 +415,7 @@ static unsigned long lguest_read_cr0(void)
* the vowels have been optimized out. */
static void lguest_clts(void)
{
lazy_hcall(LHCALL_TS, 0, 0, 0);
lazy_hcall1(LHCALL_TS, 0);
current_cr0 &= ~X86_CR0_TS;
}
......@@ -418,7 +437,7 @@ static bool cr3_changed = false;
static void lguest_write_cr3(unsigned long cr3)
{
lguest_data.pgdir = cr3;
lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0);
lazy_hcall1(LHCALL_NEW_PGTABLE, cr3);
cr3_changed = true;
}
......@@ -493,7 +512,7 @@ static void lguest_write_cr4(unsigned long val)
static void lguest_pte_update(struct mm_struct *mm, unsigned long addr,
pte_t *ptep)
{
lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, ptep->pte_low);
lazy_hcall3(LHCALL_SET_PTE, __pa(mm->pgd), addr, ptep->pte_low);
}
static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
......@@ -509,8 +528,8 @@ static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
{
*pmdp = pmdval;
lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK,
(__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
lazy_hcall2(LHCALL_SET_PMD, __pa(pmdp) & PAGE_MASK,
(__pa(pmdp) & (PAGE_SIZE - 1)) / 4);
}
/* There are a couple of legacy places where the kernel sets a PTE, but we
......@@ -526,7 +545,7 @@ static void lguest_set_pte(pte_t *ptep, pte_t pteval)
{
*ptep = pteval;
if (cr3_changed)
lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
lazy_hcall1(LHCALL_FLUSH_TLB, 1);
}
/* Unfortunately for Lguest, the pv_mmu_ops for page tables were based on
......@@ -542,7 +561,7 @@ static void lguest_set_pte(pte_t *ptep, pte_t pteval)
static void lguest_flush_tlb_single(unsigned long addr)
{
/* Simply set it to zero: if it was not, it will fault back in. */
lazy_hcall(LHCALL_SET_PTE, lguest_data.pgdir, addr, 0);
lazy_hcall3(LHCALL_SET_PTE, lguest_data.pgdir, addr, 0);
}
/* This is what happens after the Guest has removed a large number of entries.
......@@ -550,7 +569,7 @@ static void lguest_flush_tlb_single(unsigned long addr)
* have changed, ie. virtual addresses below PAGE_OFFSET. */
static void lguest_flush_tlb_user(void)
{
lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0);
lazy_hcall1(LHCALL_FLUSH_TLB, 0);
}
/* This is called when the kernel page tables have changed. That's not very
......@@ -558,7 +577,7 @@ static void lguest_flush_tlb_user(void)
* slow), so it's worth separating this from the user flushing above. */
static void lguest_flush_tlb_kernel(void)
{
lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
lazy_hcall1(LHCALL_FLUSH_TLB, 1);
}
/*
......@@ -695,7 +714,7 @@ static int lguest_clockevent_set_next_event(unsigned long delta,
}
/* Please wake us this far in the future. */
hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
kvm_hypercall1(LHCALL_SET_CLOCKEVENT, delta);
return 0;
}
......@@ -706,7 +725,7 @@ static void lguest_clockevent_set_mode(enum clock_event_mode mode,
case CLOCK_EVT_MODE_UNUSED:
case CLOCK_EVT_MODE_SHUTDOWN:
/* A 0 argument shuts the clock down. */
hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0);
kvm_hypercall0(LHCALL_SET_CLOCKEVENT);
break;
case CLOCK_EVT_MODE_ONESHOT:
/* This is what we expect. */
......@@ -781,8 +800,8 @@ static void lguest_time_init(void)
static void lguest_load_sp0(struct tss_struct *tss,
struct thread_struct *thread)
{
lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->sp0,
THREAD_SIZE/PAGE_SIZE);
lazy_hcall3(LHCALL_SET_STACK, __KERNEL_DS | 0x1, thread->sp0,
THREAD_SIZE / PAGE_SIZE);
}
/* Let's just say, I wouldn't do debugging under a Guest. */
......@@ -855,7 +874,7 @@ static void set_lguest_basic_apic_ops(void)
/* STOP! Until an interrupt comes in. */
static void lguest_safe_halt(void)
{
hcall(LHCALL_HALT, 0, 0, 0);
kvm_hypercall0(LHCALL_HALT);
}
/* The SHUTDOWN hypercall takes a string to describe what's happening, and
......@@ -865,7 +884,8 @@ static void lguest_safe_halt(void)
* rather than virtual addresses, so we use __pa() here. */
static void lguest_power_off(void)
{
hcall(LHCALL_SHUTDOWN, __pa("Power down"), LGUEST_SHUTDOWN_POWEROFF, 0);
kvm_hypercall2(LHCALL_SHUTDOWN, __pa("Power down"),
LGUEST_SHUTDOWN_POWEROFF);
}
/*
......@@ -875,7 +895,7 @@ static void lguest_power_off(void)
*/
static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
{
hcall(LHCALL_SHUTDOWN, __pa(p), LGUEST_SHUTDOWN_POWEROFF, 0);
kvm_hypercall2(LHCALL_SHUTDOWN, __pa(p), LGUEST_SHUTDOWN_POWEROFF);
/* The hcall won't return, but to keep gcc happy, we're "done". */
return NOTIFY_DONE;
}
......@@ -916,7 +936,7 @@ static __init int early_put_chars(u32 vtermno, const char *buf, int count)
len = sizeof(scratch) - 1;
scratch[len] = '\0';
memcpy(scratch, buf, len);
hcall(LHCALL_NOTIFY, __pa(scratch), 0, 0);
kvm_hypercall1(LHCALL_NOTIFY, __pa(scratch));
/* This routine returns the number of bytes actually written. */
return len;
......@@ -926,7 +946,7 @@ static __init int early_put_chars(u32 vtermno, const char *buf, int count)
* Launcher to reboot us. */
static void lguest_restart(char *reason)
{
hcall(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART, 0);
kvm_hypercall2(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART);
}
/*G:050
......
......@@ -27,8 +27,8 @@ ENTRY(lguest_entry)
/* We make the "initialization" hypercall now to tell the Host about
* us, and also find out where it put our page tables. */
movl $LHCALL_LGUEST_INIT, %eax
movl $lguest_data - __PAGE_OFFSET, %edx
int $LGUEST_TRAP_ENTRY
movl $lguest_data - __PAGE_OFFSET, %ebx
.byte 0x0f,0x01,0xc1 /* KVM_HYPERCALL */
/* Set up the initial stack so we can run C code. */
movl $(init_thread_union+THREAD_SIZE),%esp
......
......@@ -288,9 +288,10 @@ static int direct_trap(unsigned int num)
/* The Host needs to see page faults (for shadow paging and to save the
* fault address), general protection faults (in/out emulation) and
* device not available (TS handling), and of course, the hypercall
* trap. */
return num != 14 && num != 13 && num != 7 && num != LGUEST_TRAP_ENTRY;
* device not available (TS handling), invalid opcode fault (kvm hcall),
* and of course, the hypercall trap. */
return num != 14 && num != 13 && num != 7 &&
num != 6 && num != LGUEST_TRAP_ENTRY;
}
/*:*/
......
......@@ -161,7 +161,7 @@ static void set_status(struct virtio_device *vdev, u8 status)
/* We set the status. */
to_lgdev(vdev)->desc->status = status;
hcall(LHCALL_NOTIFY, (max_pfn<<PAGE_SHIFT) + offset, 0, 0);
kvm_hypercall1(LHCALL_NOTIFY, (max_pfn << PAGE_SHIFT) + offset);
}
static void lg_set_status(struct virtio_device *vdev, u8 status)
......@@ -209,7 +209,7 @@ static void lg_notify(struct virtqueue *vq)
* virtqueue structure. */
struct lguest_vq_info *lvq = vq->priv;
hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0);
kvm_hypercall1(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT);
}
/* An extern declaration inside a C file is bad form. Don't do it. */
......
......@@ -290,6 +290,57 @@ static int emulate_insn(struct lg_cpu *cpu)
return 1;
}
/* Our hypercalls mechanism used to be based on direct software interrupts.
* After Anthony's "Refactor hypercall infrastructure" kvm patch, we decided to
* change over to using kvm hypercalls.
*
* KVM_HYPERCALL is actually a "vmcall" instruction, which generates an invalid
* opcode fault (fault 6) on non-VT cpus, so the easiest solution seemed to be
* an *emulation approach*: if the fault was really produced by an hypercall
* (is_hypercall() does exactly this check), we can just call the corresponding
* hypercall host implementation function.
*
* But these invalid opcode faults are notably slower than software interrupts.
* So we implemented the *patching (or rewriting) approach*: every time we hit
* the KVM_HYPERCALL opcode in Guest code, we patch it to the old "int 0x1f"
* opcode, so next time the Guest calls this hypercall it will use the
* faster trap mechanism.
*
* Matias even benchmarked it to convince you: this shows the average cycle
* cost of a hypercall. For each alternative solution mentioned above we've
* made 5 runs of the benchmark:
*
* 1) direct software interrupt: 2915, 2789, 2764, 2721, 2898
* 2) emulation technique: 3410, 3681, 3466, 3392, 3780
* 3) patching (rewrite) technique: 2977, 2975, 2891, 2637, 2884
*
* One two-line function is worth a 20% hypercall speed boost!
*/
static void rewrite_hypercall(struct lg_cpu *cpu)
{
/* This are the opcodes we use to patch the Guest. The opcode for "int
* $0x1f" is "0xcd 0x1f" but vmcall instruction is 3 bytes long, so we
* complete the sequence with a NOP (0x90). */
u8 insn[3] = {0xcd, 0x1f, 0x90};
__lgwrite(cpu, guest_pa(cpu, cpu->regs->eip), insn, sizeof(insn));
}
static bool is_hypercall(struct lg_cpu *cpu)
{
u8 insn[3];
/* This must be the Guest kernel trying to do something.
* The bottom two bits of the CS segment register are the privilege
* level. */
if ((cpu->regs->cs & 3) != GUEST_PL)
return false;
/* Is it a vmcall? */
__lgread(cpu, insn, guest_pa(cpu, cpu->regs->eip), sizeof(insn));
return insn[0] == 0x0f && insn[1] == 0x01 && insn[2] == 0xc1;
}
/*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
void lguest_arch_handle_trap(struct lg_cpu *cpu)
{
......@@ -337,7 +388,7 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
break;
case 32 ... 255:
/* These values mean a real interrupt occurred, in which case
* the Host handler has already been run. We just do a
* the Host handler has already been run. We just do a
* friendly check if another process should now be run, then
* return to run the Guest again */
cond_resched();
......@@ -347,6 +398,15 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
* up the pointer now to indicate a hypercall is pending. */
cpu->hcall = (struct hcall_args *)cpu->regs;
return;
case 6:
/* kvm hypercalls trigger an invalid opcode fault (6).
* We need to check if ring == GUEST_PL and
* faulting instruction == vmcall. */
if (is_hypercall(cpu)) {
rewrite_hypercall(cpu);
return;
}
break;
}
/* We didn't handle the trap, so it needs to go to the Guest. */
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment