On Thu, Jul 21, 2022 at 01:29:34AM +0000, Sean Christopherson wrote:
> On Fri, Jun 24, 2022, Ricardo Koller wrote:
> > Add a new test for stage 2 faults when using different combinations of
> > guest accesses (e.g., write, S1PTW), backing source type (e.g., anon)
> > and types of faults (e.g., read on hugetlbfs with a hole). The next
> > commits will add different handling methods and more faults (e.g., uffd
> > and dirty logging). This first commit starts by adding two sanity checks
> > for all types of accesses: AF setting by the hw, and accessing memslots
> > with holes.
> >
> > Signed-off-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
> > ---
>
> ...
>
> > +/*
> > + * Create a memslot for test data (memslot[TEST]) and another one for PT
> > + * tables (memslot[PT]). This diagram show the resulting guest virtual and
> > + * physical address space when using 4K backing pages for the memslots, and
> > + * 4K guest pages.
> > + *
> > + * Guest physical Guest virtual
> > + *
> > + * | | | |
> > + * | | | |
> > + * +--------------+ +-------------+
> > + * max_gfn - 0x1000 | TEST memslot |<---------+ test data | 0xc0000000
> > + * +--------------+ +-------------+
> > + * max_gfn - 0x2000 | gap |<---------+ gap | 0xbffff000
> > + * +--------------+ +-------------+
> > + * | | | |
> > + * | | | |
> > + * | PT memslot | | |
> > + * | | +-------------+
> > + * max_gfn - 0x6000 | |<----+ | |
> > + * +--------------+ | | |
> > + * | | | | PTE for the |
> > + * | | | | test data |
> > + * | | +----+ page | 0xb0000000
> > + * | | +-------------+
> > + * | | | |
> > + * | | | |
> > + *
> > + * Using different guest page sizes or backing pages will result in the
> > + * same layout but at different addresses. In particular, the memslot
> > + * sizes need to be multiple of the backing page sizes (e.g., 2MB).
> > + */
> > +static void setup_memslots(struct kvm_vm *vm, enum vm_guest_mode mode,
> > + struct test_params *p)
> > +{
> > + uint64_t backing_page_size = get_backing_src_pagesz(p->src_type);
> > + uint64_t guest_page_size = vm_guest_mode_params[mode].page_size;
> > + struct test_desc *test = p->test_desc;
> > + uint64_t gap_gpa;
> > + uint64_t alignment;
> > + int i;
> > +
> > + memslot[TEST].size = align_up(guest_page_size, backing_page_size);
> > + /*
> > + * We need one guest page for the PT table containing the PTE (for
> > + * TEST_GVA), but might need more in case the higher level PT tables
> > + * were not allocated yet.
> > + */
> > + memslot[PT].size = align_up(4 * guest_page_size, backing_page_size);
> > +
> > + for (i = 0; i < NR_MEMSLOTS; i++) {
> > + memslot[i].guest_pages = memslot[i].size / guest_page_size;
> > + memslot[i].src_type = p->src_type;
> > + }
> > +
> > + /* Place the memslots GPAs at the end of physical memory */
> > + alignment = max(backing_page_size, guest_page_size);
> > + memslot[TEST].gpa = (vm->max_gfn - memslot[TEST].guest_pages) *
> > + guest_page_size;
> > + memslot[TEST].gpa = align_down(memslot[TEST].gpa, alignment);
> > +
> > + /* Add a 1-guest_page gap between the two memslots */
> > + gap_gpa = memslot[TEST].gpa - guest_page_size;
> > + /* Map the gap so it's still adressable from the guest. */
> > + virt_pg_map(vm, TEST_GVA - guest_page_size, gap_gpa);
> > +
> > + memslot[PT].gpa = gap_gpa - memslot[PT].size;
> > + memslot[PT].gpa = align_down(memslot[PT].gpa, alignment);
> > +
> > + vm_userspace_mem_region_add(vm, p->src_type, memslot[PT].gpa,
> > + memslot[PT].idx, memslot[PT].guest_pages,
> > + test->pt_memslot_flags);
> > + vm_userspace_mem_region_add(vm, p->src_type, memslot[TEST].gpa,
> > + memslot[TEST].idx, memslot[TEST].guest_pages,
> > + test->test_memslot_flags);
> > +
> > + for (i = 0; i < NR_MEMSLOTS; i++)
> > + memslot[i].hva = addr_gpa2hva(vm, memslot[i].gpa);
> > +
> > + /* Map the test TEST_GVA using the PT memslot. */
> > + _virt_pg_map(vm, TEST_GVA, memslot[TEST].gpa, MT_NORMAL,
> > + TEST_PT_SLOT_INDEX);
>
> Use memslot[TEST].idx instead of TEST_PT_SLOT_INDEX to be consistent, though my
> preference would be to avoid this API.
>
> IIUC, the goal is to test different backing stores for the memory the guest uses
> for it's page tables. But do we care about testing that a single guest's page
> tables are backed with different types concurrently?
This test creates a new VM for each subtest, so an API like that would
definitely make this code simpler/nicer.
> If we don't care, and maybe
> even if we do, then my preference would be to enhance the __vm_create family of
> helpers to allow for specifying what backing type should be used for page tables,
> i.e. associate the info the VM instead of passing it around the stack.
>
> One idea would be to do something like David Matlack suggested a while back and
> replace extra_mem_pages with a struct, e.g. struct kvm_vm_mem_params That struct
> can then provide the necessary knobs to control how memory is allocated. And then
> the lib can provide a global
>
> struct kvm_vm_mem_params kvm_default_vm_mem_params;
>
I like this idea, passing the info at vm creation.
What about dividing the changes in two.
1. Will add the struct to "__vm_create()" as part of this
series, and then use it in this commit. There's only one user
dirty_log_test.c: vm = __vm_create(mode, 1, extra_mem_pages);
so that would avoid having to touch every test as part of this patchset.
2. I can then send another series to add support for all the other
vm_create() functions.
Alternatively, I can send a new series that does 1 and 2 afterwards.
WDYT?
> or whatever (probably a shorter name) for the tests that don't care. And then
> down the road, if someone wants to control the backing type for code vs. data,
> we could and those flags to kvm_vm_mem_params and add vm_vaddr_alloc() wrappers
> to alloc code vs. data (with a default to data?).
>
> I don't like the param approach because it bleeds implementation details that
> really shouldn't matter, e.g. which memslot is the default, into tests. And it's
> not very easy to use, e.g. if a different test wants to do something similar,
> it would have to create its own memslot, populate the tables, etc...
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