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    SubjectRe: [PATCH v8 08/40] x86/sev: Check the vmpl level
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    On 12/20/21 12:10 PM, Borislav Petkov wrote:
    > On Fri, Dec 17, 2021 at 04:33:02PM -0600, Tom Lendacky wrote:
    >>>>>> + * There is no straightforward way to query the current VMPL level. The
    >>>>>> + * simplest method is to use the RMPADJUST instruction to change a page
    >>>>>> + * permission to a VMPL level-1, and if the guest kernel is launched at
    >>>>>> + * a level <= 1, then RMPADJUST instruction will return an error.
    >>>>> Perhaps a nit. When you say "level <= 1", do you mean a level lower than or
    >>>>> equal to 1 semantically, or numerically?
    >>>
    >>> Its numerically, please see the AMD APM vol 3.
    >>
    >> Actually it is not numerically... if it was numerically, then 0 <= 1 would
    >> return an error, but VMPL0 is the highest permission level.
    >
    > Just write in that comment exactly what this function does:
    >
    > "RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
    > higher) privilege level. Here, clear the VMPL1 permission mask of the
    > GHCB page. If the guest is not running at VMPL0, this will fail.
    >
    > If the guest is running at VMP0, it will succeed. Even if that operation
    > modifies permission bits, it is still ok to do currently because Linux
    > SNP guests are supported only on VMPL0 so VMPL1 or higher permission
    > masks changing is a don't-care."
    >
    > and then everything is clear wrt numbering, privilege, etc.
    >
    > Ok?
    >

    Noted.

    thanks

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