From: FF <figure1802@126.com>
To: linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: A quick question about ASID on KPTI
Date: Tue, 3 Mar 2020 09:08:00 +0800 (CST) [thread overview]
Message-ID: <c427a03.eed.1709def7541.Coremail.figure1802@126.com> (raw)
hi folks,
i am look at some patches about the KPTI on ARM64, a quick question about the ASDI on KPTI:
On KPIT, it will allocate a pairs ASID for a process, when the process running on kernel space, it will set the even ASID into TTBR1 register in tramp_map_kernel function, when the process running on User space, it will set the odd ASID into the TTBR1 register in tramp_unmap_kernel function.
my question is, when the process running in kernel space, if the process want to access the userspace address by copy_to/from_user(), the CPU will look-up the TLB with even ASID or odd ASID? if it use even ASID to look-up TLB for userspace, it will always TLB miss, that will be performance impact. is it right? pls correct me if i am wrong.
Best
Ben
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next reply other threads:[~2020-03-03 1:08 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-03 1:08 FF [this message]
2020-03-03 9:45 ` A quick question about ASID on KPTI Catalin Marinas
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