On Mon, May 23, 2022 at 10:37 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Fri, May 20, 2022, Mingwei Zhang wrote:
> > On Mon, May 16, 2022 at 4:24 PM David Matlack <dmatlack@xxxxxxxxxx> wrote:
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index e089db822c12..5e2e75014256 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -369,14 +369,31 @@ static inline void *mmu_memory_cache_alloc_obj(struct kvm_mmu_memory_cache *mc,
> > > return (void *)__get_free_page(gfp_flags);
> > > }
> > >
> > > -int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min)
> > > +static int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, int min)
> > > {
> > > + gfp_t gfp = GFP_KERNEL_ACCOUNT;
> > > void *obj;
> > >
> > > if (mc->nobjs >= min)
> > > return 0;
> > > - while (mc->nobjs < ARRAY_SIZE(mc->objects)) {
> > > - obj = mmu_memory_cache_alloc_obj(mc, GFP_KERNEL_ACCOUNT);
> > > +
> > > + if (unlikely(!mc->objects)) {
> > > + if (WARN_ON_ONCE(!capacity))
> > > + return -EIO;
> > > +
> > > + mc->objects = kvmalloc_array(sizeof(void *), capacity, gfp);
> > > + if (!mc->objects)
> > > + return -ENOMEM;
> > > +
> > > + mc->capacity = capacity;
> >
> > Do we want to ensure the minimum value of the capacity? I think
> > otherwise, we may more likely start using memory from GFP_ATOMIC if
> > the capacity is less than, say 5? But the minimum value seems related
> > to each cache type.
>
> Eh, if we specify a minimum, just make the arch default the minimum. That way we
> avoid adding even more magic/arbitrary numbers. E.g. for whatever reason, MIPS's
> default is '4'.
I'm not exactly sure what you had in mind Mingwei. But there is a bug
in this code if min > capacity. This function will happily return 0
after filling up the cache, even though it did not allocate min
objects. The same bug existed before this patch if min >
ARRAY_SIZE(mc->objects). I can include a separate patch to fix this
bug (e.g. WARN and return -ENOMEM if min > capacity).
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