On Wed, Sep 23, 2020 at 12:58:58PM +0800, Li RongQing wrote:
> counting of rmap entries was missed when desc->sptes is full
> and desc->more is NULL
>
> and merging two PTE_LIST_EXT-1 check as one, to avoids the
> extra comparison to give slightly optimization
Please write complete sentences, and use proper capitalization and punctuation.
It's not a big deal for short changelogs, but it's crucial for readability of
larger changelogs.
E.g.
Fix an off-by-one style bug in pte_list_add() where it failed to account
the last full set of SPTEs, i.e. when desc->sptes is full and desc->more
is NULL.
Merge the two "PTE_LIST_EXT-1" checks as part of the fix to avoid an
extra comparison.
> Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
No need to give me credit, I just nitpicked the code, identifying the bug
and the fix was all you. :-)
Thanks for the fix!
> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
Paolo,
Although it's a bug fix, I don't think this needs a Fixes / Cc:stable. The bug
only results in rmap recycling being delayed by one rmap. Stable kernels can
probably live with an off-by-one bug given that RMAP_RECYCLE_THRESHOLD is
completely arbitrary. :-)
Reviewed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
> diff with v1: merge two check as one
>
> arch/x86/kvm/mmu/mmu.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index a5d0207e7189..c4068be6bb3f 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1273,12 +1273,14 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
> } else {
> rmap_printk("pte_list_add: %p %llx many->many\n", spte, *spte);
> desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> - while (desc->sptes[PTE_LIST_EXT-1] && desc->more) {
> - desc = desc->more;
> + while (desc->sptes[PTE_LIST_EXT-1]) {
> count += PTE_LIST_EXT;
> - }
> - if (desc->sptes[PTE_LIST_EXT-1]) {
> - desc->more = mmu_alloc_pte_list_desc(vcpu);
> +
> + if (!desc->more) {
> + desc->more = mmu_alloc_pte_list_desc(vcpu);
> + desc = desc->more;
> + break;
> + }
> desc = desc->more;
> }
> for (i = 0; desc->sptes[i]; ++i)
> --
> 2.16.2
>
