hollalinux
/
linux-sg2042
mirror of https://github.com/sophgo/linux-riscv.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

KVM: PPC: Book3S HV: Fix race in reading change bit when removing HPTE 

The reference (R) and change (C) bits in a HPT entry can be set by
hardware at any time up until the HPTE is invalidated and the TLB
invalidation sequence has completed.  This means that when removing
a HPTE, we need to read the HPTE after the invalidation sequence has
completed in order to obtain reliable values of R and C.  The code
in kvmppc_do_h_remove() used to do this.  However, commit 6f22bd3265
("KVM: PPC: Book3S HV: Make HTAB code LE host aware") removed the
read after invalidation as a side effect of other changes.  This
restores the read of the HPTE after invalidation.

The user-visible effect of this bug would be that when migrating a
guest, there is a small probability that a page modified by the guest
and then unmapped by the guest might not get re-transmitted and thus
the destination might end up with a stale copy of the page.

Fixes: 6f22bd3265
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
This commit is contained in:
Paul Mackerras 2015-06-24 21:18:05 +10:00 committed by Alexander Graf
parent b4deba5c41
commit 1e5bf454f5
1 changed files with 12 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
arch/powerpc/kvm/book3s_hv_rm_mmu.c
View File

@ -421,14 +421,20 @@ long kvmppc_do_h_remove(struct kvm *kvm, unsigned long flags,
rev = real_vmalloc_addr(&kvm->arch.revmap[pte_index]);
v = pte & ~HPTE_V_HVLOCK;
if (v & HPTE_V_VALID) {
u64 pte1;
pte1 = be64_to_cpu(hpte[1]);
hpte[0] &= ~cpu_to_be64(HPTE_V_VALID);
rb = compute_tlbie_rb(v, pte1, pte_index);
rb = compute_tlbie_rb(v, be64_to_cpu(hpte[1]), pte_index);
do_tlbies(kvm, &rb, 1, global_invalidates(kvm, flags), true);
/* Read PTE low word after tlbie to get final R/C values */
remove_revmap_chain(kvm, pte_index, rev, v, pte1);
/*
* The reference (R) and change (C) bits in a HPT
* entry can be set by hardware at any time up until
* the HPTE is invalidated and the TLB invalidation
* sequence has completed. This means that when
* removing a HPTE, we need to re-read the HPTE after
* the invalidation sequence has completed in order to
* obtain reliable values of R and C.
*/
remove_revmap_chain(kvm, pte_index, rev, v,
be64_to_cpu(hpte[1]));
}
r = rev->guest_rpte & ~HPTE_GR_RESERVED;
note_hpte_modification(kvm, rev);