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Formerly, we used to maintain a per-vcpu shadow TLB and on every entry to the guest would load this array into the hardware TLB. This consumed 1280 bytes of memory (64 entries of 16 bytes plus a struct page pointer each), and also required some assembly to loop over the array on every entry. Instead of saving a copy in memory, we can just store shadow mappings directly into the hardware TLB, accepting that the host kernel will clobber these as part of the normal 440 TLB round robin. When we do that we need less than half the memory, and we have decreased the exit handling time for all guest exits, at the cost of increased number of TLB misses because the host overwrites some guest entries. These savings will be increased on processors with larger TLBs or which implement intelligent flush instructions like tlbivax (which will avoid the need to walk arrays in software). In addition to that and to the code simplification, we have a greater chance of leaving other host userspace mappings in the TLB, instead of forcing all subsequent tasks to re-fault all their mappings. Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com> Signed-off-by: Avi Kivity <avi@redhat.com>
55 lines
1.5 KiB
C
55 lines
1.5 KiB
C
/*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License, version 2, as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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* Copyright IBM Corp. 2008
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*
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* Authors: Hollis Blanchard <hollisb@us.ibm.com>
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*/
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#ifndef __ASM_44X_H__
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#define __ASM_44X_H__
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#include <linux/kvm_host.h>
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#define PPC44x_TLB_SIZE 64
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/* If the guest is expecting it, this can be as large as we like; we'd just
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* need to find some way of advertising it. */
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#define KVM44x_GUEST_TLB_SIZE 64
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struct kvmppc_44x_shadow_ref {
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struct page *page;
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u16 gtlb_index;
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u8 writeable;
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u8 tid;
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};
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struct kvmppc_vcpu_44x {
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/* Unmodified copy of the guest's TLB. */
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struct kvmppc_44x_tlbe guest_tlb[KVM44x_GUEST_TLB_SIZE];
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/* References to guest pages in the hardware TLB. */
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struct kvmppc_44x_shadow_ref shadow_refs[PPC44x_TLB_SIZE];
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struct kvm_vcpu vcpu;
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};
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static inline struct kvmppc_vcpu_44x *to_44x(struct kvm_vcpu *vcpu)
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{
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return container_of(vcpu, struct kvmppc_vcpu_44x, vcpu);
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}
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void kvmppc_set_pid(struct kvm_vcpu *vcpu, u32 new_pid);
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#endif /* __ASM_44X_H__ */
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