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    SubjectRe: [PATCH Part2 v5 00/45] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support
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    On 11/22/21 23:51, Dave Hansen wrote:
    > On 11/22/21 12:33 PM, Brijesh Singh wrote:
    >>> How do we, for example, prevent ptrace() from inducing a panic()?
    >>
    >> In the current approach, this access will induce a panic().
    >
    > That needs to get fixed before SEV-SNP is merged, IMNHO. This behavior
    > would effectively mean that any userspace given access to create SNP
    > guests would panic the kernel.
    >
    >> In general, supporting the ptrace() for the encrypted VM region is
    >> going to be difficult.
    >
    > By "supporting", do you mean doing something functional? I don't really
    > care if ptrace() to guest private memory returns -EINVAL or whatever.
    > The most important thing is not crashing the host.
    >
    > Also, as Sean mentioned, this isn't really about ptrace() itself. It's
    > really about ensuring that no kernel or devices accesses to guest
    > private memory can induce bad behavior.

    Then we need gup to block any changes from shared to guest private? I assume
    there will be the usual issues of recognizing temporary elevated refcount vs
    long-term gup, etc.

    >> The upcoming TDX work to unmap the guest memory region from the
    >> current process page table can easily extend for the SNP to cover the
    >> current limitations.

    By "current process page table" you mean userspace page tables?

    > My preference would be that we never have SEV-SNP code in the kernel
    > that can panic() the host from guest userspace. If that means waiting
    > until there's common guest unmapping infrastructure around, then I think
    > we should wait.
    >

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