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alloc: initial TryBox implementation #196

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alloc: initial TryBox implementation #196

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Commits on Feb 26, 2024

  1. alloc: initial TryBox implementation 

    Introduce the alloc submodule and the TryBox type, a fork of the
upstream alloc crate and Box type respectively. The new type behaves
exactly like Box, except it only supports fallible allocations,
meaning that users must always handle potential errors.

Users must also explicitly set the allocator to use. Using a specific
allocator by default like the standard library does is complicated.
The standard library uses whichever allocator is set as global
(via the #[global_allocator] macro), which can be accessed via a
global instance (alloc::alloc::Global). However, the global instance
is gated behind an unstable feature, and the macro cannot be
reimplemented because it is a compiler intrinsic. As a workaround,
one may add new higher level types in the future which use a specific
allocator by default.

The new type also has a few extra methods for convenience like
try_default_in(), try_clone() and try_clone_in().

Signed-off-by: Carlos López <[email protected]>
    @00xc
    00xc committed Feb 26, 2024
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  2. mm/alloc: implement Allocator for SvsmAllocator 

    In order to be used along with the new TryBox type, an allocator must
implement the Allocator trait, so implement it for the current global
allocator.

Signed-off-by: Carlos López <[email protected]>
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  3. error: add SvsmError::TryAlloc 

    Add a new variant to hold a TryAllocError from the alloc submodule.
This new error does not implement Copy, so SvsmError cannot implement
it either.

Signed-off-by: Carlos López <[email protected]>
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  4. mm: add GlobalBox implementation 

    Add a new type, GlobalBox, which wraps around the TryBox type but uses
the global SvsmAllocator transparently. The new type implements
AsRef<TryBox> and Into<TryBox>, so regular TryBox methods can also be
used on the new type.

Signed-off-by: Carlos López <[email protected]>
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  5. mm/pagetable: replace Box with GlobalBox 

    Allocate PageTablePart structs with the new fallible-allocation-aware
GlobalBox type.

Signed-off-by: Carlos López <[email protected]>
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  6. greq: replace Box with GlobalBox 

    Use the new fallible-allocation-aware GlobalBox type when allocating
SNP request messages.

Signed-off-by: Carlos López <[email protected]>
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  7. mm/vm: replace Box with GlobalBox 

    Replace uses of Box with the new fallible-allocation-aware GlobalBox
type. Unfortunately, replacing the Box used in the RB tree for
virtual mappings is very involved.

In short, the intrusive_collections crate provides an
intrusive_adapter macro, which generates a new adapter type that
handles the insertion and deletion of any type into an intrusive
collection. Sadly, this macro is only prepared to work with the smart
pointer types in the standard library. This is done by implementing
the PointerOps trait for DefaultPointerOps<T>, where T is one of the
regular smart pointer types (Rc, Arc, Box, etc.). The macro then
generates an implementation of Adapter for the newly generated type,
which uses the selected smart pointer.

We define a substitute for DefaultPointerOps, CustomPointerOps, and
implement PointerOps for CustomPointerOps<GlobalBox>. We then add a
manual implementation of Adapter for VMMAdapter, which uses GlobalBox
under the hood.

Signed-off-by: Carlos López <[email protected]>
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  8. mm/vm/mapping: replace Box with GlobalBox 

    Replace uses of Box in the mapping API with the new
fallible-allocation-aware GlobalBox type.

Signed-off-by: Carlos López <[email protected]>
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  9. sev/secrets_page: replace Box with GlobalBox 

    Use the new fallible-allocation-aware GlobalBox type when allocating
a new secrets page for the given VPML.

Signed-off-by: Carlos López <[email protected]>
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