unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
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KVM: Reduce stack usage in kvm_pv_mmu_op()

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We're in a hot path.  We can't use kmalloc() because
it might impact performance.  So, we just stick the buffer that
we need into the kvm_vcpu_arch structure.  This is used very
often, so it is not really a waste.

We also have to move the buffer structure's definition to the
arch-specific x86 kvm header.

Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Dave Hansen 2008-08-11 10:01:49 -07:00 committed by Avi Kivity
parent b772ff362e
commit 6ad18fba05
2 changed files with 18 additions and 15 deletions
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23
arch/x86/kvm/mmu.c
View file

@ -135,13 +135,6 @@ module_param(dbg, bool, 0644);
#define ACC_USER_MASK PT_USER_MASK
#define ACC_ALL (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
struct kvm_pv_mmu_op_buffer {
void *ptr;
unsigned len;
unsigned processed;
char buf[512] __aligned(sizeof(long));
};
struct kvm_rmap_desc {
u64 *shadow_ptes[RMAP_EXT];
struct kvm_rmap_desc *more;
@ -2292,18 +2285,18 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes,
gpa_t addr, unsigned long *ret)
{
int r;
struct kvm_pv_mmu_op_buffer buffer;
struct kvm_pv_mmu_op_buffer *buffer = &vcpu->arch.mmu_op_buffer;
buffer.ptr = buffer.buf;
buffer.len = min_t(unsigned long, bytes, sizeof buffer.buf);
buffer.processed = 0;
buffer->ptr = buffer->buf;
buffer->len = min_t(unsigned long, bytes, sizeof buffer->buf);
buffer->processed = 0;
r = kvm_read_guest(vcpu->kvm, addr, buffer.buf, buffer.len);
r = kvm_read_guest(vcpu->kvm, addr, buffer->buf, buffer->len);
if (r)
goto out;
while (buffer.len) {
r = kvm_pv_mmu_op_one(vcpu, &buffer);
while (buffer->len) {
r = kvm_pv_mmu_op_one(vcpu, buffer);
if (r < 0)
goto out;
if (r == 0)
@ -2312,7 +2305,7 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes,
r = 1;
out:
*ret = buffer.processed;
*ret = buffer->processed;
return r;
}

10
include/asm-x86/kvm_host.h
View file

@ -201,6 +201,13 @@ struct kvm_mmu_page {
};
};
struct kvm_pv_mmu_op_buffer {
void *ptr;
unsigned len;
unsigned processed;
char buf[512] __aligned(sizeof(long));
};
/*
* x86 supports 3 paging modes (4-level 64-bit, 3-level 64-bit, and 2-level
* 32-bit). The kvm_mmu structure abstracts the details of the current mmu
@ -248,6 +255,9 @@ struct kvm_vcpu_arch {
bool tpr_access_reporting;
struct kvm_mmu mmu;
/* only needed in kvm_pv_mmu_op() path, but it's hot so
* put it here to avoid allocation */
struct kvm_pv_mmu_op_buffer mmu_op_buffer;
struct kvm_mmu_memory_cache mmu_pte_chain_cache;
struct kvm_mmu_memory_cache mmu_rmap_desc_cache;