Re: [Xen-devel] [PATCH 2/3] x86/vpmu: Decrement vpmu_count early in vpmu_destroy()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 13/02/17 02:29, Boris Ostrovsky wrote:
> vpmu_count should be decremented even if VPMU_CONTEXT_ALLOCATED
> is not set because on Intel processors the context is allocated
> lazily and, in fact, might never happen.
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

The code in vpmu_initialise() already subtracts 1 from the vpmu_count in
the Intel case.

Won't this now cause an underflow when shutting down a VM which didn't
enable vpmu to start with?

~Andrew

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