On Fri, Aug 16, 2024 at 04:38:48PM +0100, Catalin Marinas wrote: > On Fri, Aug 16, 2024 at 02:52:28PM +0000, Edgecombe, Rick P wrote: > > On the x86 side, we don't have a shadow stack access CMPXCHG. We will have to > > GUP and do a normal CMPXCHG off of the direct map to handle it fully properly in > > any case (CLONE_VM or not). > I guess we could do the same here and for the arm64 gcs_consume_token(). > Basically get_user_page_vma_remote() gives us the page together with the > vma that you mentioned needs checking. We can then do a cmpxchg directly > on the page_address(). It's probably faster anyway than doing GUP twice. There was some complication with get_user_page_vma_remote() while I was working on an earlier version which meant I didn't use it, though with adding checking of VMAs perhaps whatever it was isn't such an issue any more.
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