Re: [PATCH v7 1/6] KVM: arm64: Introduce hyp_alloc_private_va_range()

[Kalesh Singh <kaleshsingh@google.com>]

On Sun, Apr 10, 2022 at 11:52 PM Marc Zyngier <maz@kernel.org> wrote:
>
> On Fri, 08 Apr 2022 21:03:24 +0100,
> Kalesh Singh <kaleshsingh@google.com> wrote:
> >
> > hyp_alloc_private_va_range() can be used to reserve private VA ranges
> > in the nVHE hypervisor. Allocations are aligned based on the order of
> > the requested size.
> >
> > This will be used to implement stack guard pages for KVM nVHE hypervisor
> > (nVHE Hyp mode / not pKVM), in a subsequent patch in the series.
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> > Tested-by: Fuad Tabba <tabba@google.com>
> > Reviewed-by: Fuad Tabba <tabba@google.com>
> > ---
> >
> > Changes in v7:
> >   - Add Fuad's Reviewed-by and Tested-by tags.
> >
> > Changes in v6:
> >   - Update kernel-doc for hyp_alloc_private_va_range()
> >     and add return description, per Stephen
> >   - Update hyp_alloc_private_va_range() to return an int error code,
> >     per Stephen
> >   - Replace IS_ERR() checks with IS_ERR_VALUE() check, per Stephen
> >   - Clean up goto, per Stephen
> >
> > Changes in v5:
> >   - Align private allocations based on the order of their size, per Marc
> >
> > Changes in v4:
> >   - Handle null ptr in hyp_alloc_private_va_range() and replace
> >     IS_ERR_OR_NULL checks in callers with IS_ERR checks, per Fuad
> >   - Fix kernel-doc comments format, per Fuad
> >
> > Changes in v3:
> >   - Handle null ptr in IS_ERR_OR_NULL checks, per Mark
> >
> >
> >  arch/arm64/include/asm/kvm_mmu.h |  1 +
> >  arch/arm64/kvm/mmu.c             | 66 +++++++++++++++++++++-----------
> >  2 files changed, 45 insertions(+), 22 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> > index 74735a864eee..a50cbb5ba402 100644
> > --- a/arch/arm64/include/asm/kvm_mmu.h
> > +++ b/arch/arm64/include/asm/kvm_mmu.h
> > @@ -154,6 +154,7 @@ static __always_inline unsigned long __kern_hyp_va(unsigned long v)
> >  int kvm_share_hyp(void *from, void *to);
> >  void kvm_unshare_hyp(void *from, void *to);
> >  int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
> > +int hyp_alloc_private_va_range(size_t size, unsigned long *haddr);
> >  int create_hyp_io_mappings(phys_addr_t phys_addr, size_t size,
> >                          void __iomem **kaddr,
> >                          void __iomem **haddr);
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 0d19259454d8..3d3efea4e991 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -457,23 +457,22 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
> >       return 0;
> >  }
> >
> > -static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> > -                                     unsigned long *haddr,
> > -                                     enum kvm_pgtable_prot prot)
> > +
> > +/**
> > + * hyp_alloc_private_va_range - Allocates a private VA range.
> > + * @size:    The size of the VA range to reserve.
> > + * @haddr:   The hypervisor virtual start address of the allocation.
> > + *
> > + * The private virtual address (VA) range is allocated below io_map_base
> > + * and aligned based on the order of @size.
> > + *
> > + * Return: 0 on success or negative error code on failure.
> > + */
> > +int hyp_alloc_private_va_range(size_t size, unsigned long *haddr)
> >  {
> >       unsigned long base;
> >       int ret = 0;
> >
> > -     if (!kvm_host_owns_hyp_mappings()) {
> > -             base = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
> > -                                      phys_addr, size, prot);
> > -             if (IS_ERR_OR_NULL((void *)base))
> > -                     return PTR_ERR((void *)base);
> > -             *haddr = base;
> > -
> > -             return 0;
> > -     }
> > -
> >       mutex_lock(&kvm_hyp_pgd_mutex);
> >
> >       /*
> > @@ -484,30 +483,53 @@ static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> >        *
> >        * The allocated size is always a multiple of PAGE_SIZE.
> >        */
> > -     size = PAGE_ALIGN(size + offset_in_page(phys_addr));
> > -     base = io_map_base - size;
> > +     base = io_map_base - PAGE_ALIGN(size);
> > +
> > +     /* Align the allocation based on the order of its size */
> > +     base = ALIGN_DOWN(base, PAGE_SIZE << get_order(size));
> >
> >       /*
> >        * Verify that BIT(VA_BITS - 1) hasn't been flipped by
> >        * allocating the new area, as it would indicate we've
> >        * overflowed the idmap/IO address range.
> >        */
> > -     if ((base ^ io_map_base) & BIT(VA_BITS - 1))
> > +     if (!base || (base ^ io_map_base) & BIT(VA_BITS - 1))
>
> I don't get this '!base' check. Why isn't it encompassed by the
> 'VA_BITS - 1' flip check?

Hi Marc, You're right. The flip check handles this as well. I’ll drop
in the next version.

>
> >               ret = -ENOMEM;
> >       else
> > -             io_map_base = base;
> > +             *haddr = io_map_base = base;
> >
> >       mutex_unlock(&kvm_hyp_pgd_mutex);
> >
> > +     return ret;
> > +}
> > +
> > +static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> > +                                     unsigned long *haddr,
> > +                                     enum kvm_pgtable_prot prot)
> > +{
> > +     unsigned long addr;
> > +     int ret = 0;
> > +
> > +     if (!kvm_host_owns_hyp_mappings()) {
> > +             addr = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
> > +                                      phys_addr, size, prot);
> > +             if (IS_ERR_VALUE(addr))
> > +                     return addr;
> > +             *haddr = addr;
> > +
> > +             return 0;
> > +     }
> > +
> > +     size += offset_in_page(phys_addr);
>
> This hardly makes any sense on its own. I get it that it is still
> doing the right thing as hyp_alloc_private_va_range() will fix it up,
> but I'd rather you keep the PAGE_ALIGN() here, even if it ends up
> being duplicated.

Ack

Thanks,
Kalesh

>
> > +     ret = hyp_alloc_private_va_range(size, &addr);
> >       if (ret)
> > -             goto out;
> > +             return ret;
> >
> > -     ret = __create_hyp_mappings(base, size, phys_addr, prot);
> > +     ret = __create_hyp_mappings(addr, size, phys_addr, prot);
> >       if (ret)
> > -             goto out;
> > +             return ret;
> >
> > -     *haddr = base + offset_in_page(phys_addr);
> > -out:
> > +     *haddr = addr + offset_in_page(phys_addr);
> >       return ret;
> >  }
> >
>
> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.