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KVM: x86 emulator: prefetch up to 15 bytes of the instruction executed

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Instead of fetching one byte at a time, prefetch 15 bytes (or until the next
page boundary) to avoid guest page table walks.

Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Avi Kivity 2007-11-20 13:15:52 +02:00
parent 93a0039c8d
commit 6226686954
2 changed files with 43 additions and 2 deletions
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38
drivers/kvm/x86_emulate.c
View File

@ -414,8 +414,7 @@ static u16 twobyte_table[256] = {
/* Fetch next part of the instruction being emulated. */
#define insn_fetch(_type, _size, _eip) \
({ unsigned long _x; \
rc = ops->read_std((unsigned long)(_eip) + ctxt->cs_base, &_x, \
(_size), ctxt->vcpu); \
rc = do_insn_fetch(ctxt, ops, (_eip), &_x, (_size)); \
if (rc != 0) \
goto done; \
(_eip) += (_size); \
@ -446,6 +445,41 @@ static u16 twobyte_table[256] = {
register_address_increment(c->eip, rel); \
} while (0)
static int do_fetch_insn_byte(struct x86_emulate_ctxt *ctxt,
struct x86_emulate_ops *ops,
unsigned long linear, u8 *dest)
{
struct fetch_cache *fc = &ctxt->decode.fetch;
int rc;
int size;
if (linear < fc->start || linear >= fc->end) {
size = min(15UL, PAGE_SIZE - offset_in_page(linear));
rc = ops->read_std(linear, fc->data, size, ctxt->vcpu);
if (rc)
return rc;
fc->start = linear;
fc->end = linear + size;
}
*dest = fc->data[linear - fc->start];
return 0;
}
static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,
struct x86_emulate_ops *ops,
unsigned long eip, void *dest, unsigned size)
{
int rc = 0;
eip += ctxt->cs_base;
while (size--) {
rc = do_fetch_insn_byte(ctxt, ops, eip++, dest++);
if (rc)
return rc;
}
return 0;
}
/*
* Given the 'reg' portion of a ModRM byte, and a register block, return a
* pointer into the block that addresses the relevant register.

7
drivers/kvm/x86_emulate.h
View File

@ -108,6 +108,12 @@ struct operand {
unsigned long val, orig_val, *ptr;
};
struct fetch_cache {
u8 data[15];
unsigned long start;
unsigned long end;
};
struct decode_cache {
u8 twobyte;
u8 b;
@ -130,6 +136,7 @@ struct decode_cache {
u8 use_modrm_ea;
unsigned long modrm_ea;
unsigned long modrm_val;
struct fetch_cache fetch;
};
struct x86_emulate_ctxt {