Re: [RFC PATCH v5 01/29] KVM: selftests: Add function to allow one-to-one GVA to GPA mappings

[Sagi Shahar <sagis@google.com>]

On Tue, Feb 20, 2024 at 7:43 PM Binbin Wu <binbin.wu@linux.intel.com> wrote:
>
>
>
> On 12/13/2023 4:46 AM, Sagi Shahar wrote:
> > From: Ackerley Tng <ackerleytng@google.com>
> >
> > One-to-one GVA to GPA mappings can be used in the guest to set up boot
> > sequences during which paging is enabled, hence requiring a transition
> > from using physical to virtual addresses in consecutive instructions.
> >
> > Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> > Signed-off-by: Ryan Afranji <afranji@google.com>
> > Signed-off-by: Sagi Shahar <sagis@google.com>
> > ---
> >   .../selftests/kvm/include/kvm_util_base.h     |  2 +
> >   tools/testing/selftests/kvm/lib/kvm_util.c    | 63 ++++++++++++++++---
> >   2 files changed, 55 insertions(+), 10 deletions(-)
> >
> > diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> > index 1426e88ebdc7..c2e5c5f25dfc 100644
> > --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> > +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> > @@ -564,6 +564,8 @@ vm_vaddr_t vm_vaddr_alloc(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min);
> >   vm_vaddr_t __vm_vaddr_alloc(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min,
> >                           enum kvm_mem_region_type type);
> >   vm_vaddr_t vm_vaddr_alloc_shared(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min);
> > +vm_vaddr_t vm_vaddr_alloc_1to1(struct kvm_vm *vm, size_t sz,
> > +                            vm_vaddr_t vaddr_min, uint32_t data_memslot);
> >   vm_vaddr_t vm_vaddr_alloc_pages(struct kvm_vm *vm, int nr_pages);
> >   vm_vaddr_t __vm_vaddr_alloc_page(struct kvm_vm *vm,
> >                                enum kvm_mem_region_type type);
> > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> > index febc63d7a46b..4f1ae0f1eef0 100644
> > --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > @@ -1388,17 +1388,37 @@ vm_vaddr_t vm_vaddr_unused_gap(struct kvm_vm *vm, size_t sz,
> >       return pgidx_start * vm->page_size;
> >   }
> >
> > +/*
> > + * VM Virtual Address Allocate Shared/Encrypted
> > + *
> > + * Input Args:
> > + *   vm - Virtual Machine
> > + *   sz - Size in bytes
> > + *   vaddr_min - Minimum starting virtual address
> > + *   paddr_min - Minimum starting physical address
> > + *   data_memslot - memslot number to allocate in
> > + *   encrypt - Whether the region should be handled as encrypted
> > + *
> > + * Output Args: None
> > + *
> > + * Return:
> > + *   Starting guest virtual address
> > + *
> > + * Allocates at least sz bytes within the virtual address space of the vm
> > + * given by vm.  The allocated bytes are mapped to a virtual address >=
> > + * the address given by vaddr_min.  Note that each allocation uses a
> > + * a unique set of pages, with the minimum real allocation being at least
> > + * a page.
> > + */
> >   static vm_vaddr_t ____vm_vaddr_alloc(struct kvm_vm *vm, size_t sz,
> > -                                  vm_vaddr_t vaddr_min,
> > -                                  enum kvm_mem_region_type type,
> > -                                  bool encrypt)
> > +                                  vm_vaddr_t vaddr_min, vm_paddr_t paddr_min,
> > +                                  uint32_t data_memslot, bool encrypt)
> >   {
> >       uint64_t pages = (sz >> vm->page_shift) + ((sz % vm->page_size) != 0);
> >
> >       virt_pgd_alloc(vm);
> > -     vm_paddr_t paddr = _vm_phy_pages_alloc(vm, pages,
> > -                                           KVM_UTIL_MIN_PFN * vm->page_size,
> > -                                           vm->memslots[type], encrypt);
> > +     vm_paddr_t paddr = _vm_phy_pages_alloc(vm, pages, paddr_min,
> > +                                            data_memslot, encrypt);
> >
> >       /*
> >        * Find an unused range of virtual page addresses of at least
> > @@ -1408,8 +1428,7 @@ static vm_vaddr_t ____vm_vaddr_alloc(struct kvm_vm *vm, size_t sz,
> >
> >       /* Map the virtual pages. */
> >       for (vm_vaddr_t vaddr = vaddr_start; pages > 0;
> > -             pages--, vaddr += vm->page_size, paddr += vm->page_size) {
> > -
> > +          pages--, vaddr += vm->page_size, paddr += vm->page_size) {
> >               virt_pg_map(vm, vaddr, paddr);
> >
> >               sparsebit_set(vm->vpages_mapped, vaddr >> vm->page_shift);
> > @@ -1421,12 +1440,16 @@ static vm_vaddr_t ____vm_vaddr_alloc(struct kvm_vm *vm, size_t sz,
> >   vm_vaddr_t __vm_vaddr_alloc(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min,
> >                           enum kvm_mem_region_type type)
> >   {
> > -     return ____vm_vaddr_alloc(vm, sz, vaddr_min, type, vm->protected);
> > +     return ____vm_vaddr_alloc(vm, sz, vaddr_min,
> > +                               KVM_UTIL_MIN_PFN * vm->page_size,
> > +                               vm->memslots[type], vm->protected);
> >   }
> >
> >   vm_vaddr_t vm_vaddr_alloc_shared(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min)
> >   {
> > -     return ____vm_vaddr_alloc(vm, sz, vaddr_min, MEM_REGION_TEST_DATA, false);
> > +     return ____vm_vaddr_alloc(vm, sz, vaddr_min,
> > +                               KVM_UTIL_MIN_PFN * vm->page_size,
> > +                               vm->memslots[MEM_REGION_TEST_DATA], false);
> >   }
> >
> >   /*
> > @@ -1453,6 +1476,26 @@ vm_vaddr_t vm_vaddr_alloc(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min)
> >       return __vm_vaddr_alloc(vm, sz, vaddr_min, MEM_REGION_TEST_DATA);
> >   }
> >
> > +/**
> > + * Allocate memory in @vm of size @sz in memslot with id @data_memslot,
> > + * beginning with the desired address of @vaddr_min.
> > + *
> > + * If there isn't enough memory at @vaddr_min, find the next possible address
> > + * that can meet the requested size in the given memslot.
> > + *
> > + * Return the address where the memory is allocated.
> > + */
> > +vm_vaddr_t vm_vaddr_alloc_1to1(struct kvm_vm *vm, size_t sz,
> > +                            vm_vaddr_t vaddr_min, uint32_t data_memslot)
> > +{
> > +     vm_vaddr_t gva = ____vm_vaddr_alloc(vm, sz, vaddr_min,
> > +                                         (vm_paddr_t)vaddr_min, data_memslot,
> > +                                         vm->protected);
> > +     TEST_ASSERT_EQ(gva, addr_gva2gpa(vm, gva));
>
> How can this be guaranteed?
> For ____vm_vaddr_alloc(), generically there is no enforcement about the
> identity of virtual and physical address.

The problem is that if the allocation won't be 1-to-1 the tests won't
work. So we figured it's better to fail early.
The way this is used in practice generally guarantees that the mapping
can be 1-to-1 since we create these mappings at an early stage.
>
> > +
> > +     return gva;
> > +}
> > +
> >   /*
> >    * VM Virtual Address Allocate Pages
> >    *
>
>