[PATCH v4 2/4] arm64: Work around Falkor erratum 1003
From: Christopher Covington <hidden>
Date: 2017-01-30 22:09:40
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kvm, kvmarm, lkml
Hi Mark, On 01/30/2017 05:56 AM, Mark Rutland wrote:
Hi, On Fri, Jan 27, 2017 at 04:52:23PM -0500, Christopher Covington wrote:quoted
On 01/27/2017 09:38 AM, Mark Rutland wrote:quoted
On Wed, Jan 25, 2017 at 10:52:30AM -0500, Christopher Covington wrote:quoted
quoted
quoted
Replacing the above sequence with the one below will ensure that no TLB entries with an incorrect ASID are used by software. write reserved value to TTBRx_EL1[ASID] ISB write new value to TTBRx_EL1[BADDR] ISB write new value to TTBRx_EL1[ASID] ISB When the above sequence is used, page table entries using the new BADDR value may still be incorrectly allocated into the TLB using the reserved ASID. Yet this will not reduce functionality, since TLB entries incorrectly tagged with the reserved ASID will never be hit by a later instruction.I agree that there should be no explicit accesses to the VAs for these entries. So tasks should not see erroneous VAs, and we shouldn't see synchronous TLB conflict aborts. Regardless, can this allow conflicting TLB entries to be allocated to the reserved ASID? e.g. if one task has a 4K mapping at a given VA, and another has a 2M mapping which covers that VA, can both be allocated into the TLBs under the reserved ASID? Can that have any effect on asynchronous TLB lookups or page table walks, e.g. for speculated accesses?A speculative access that inserts an entry into the TLB could possibly find the conflict but will not signal it. Does that answer your question?Yes! The other case I was worried about was intermediate caching. I take it the values in TLBs are not used as part of subsequent page table walks? If so, the above sounds fine to me. Otherwise, we'll need additional TLB maintenance.
Errant TLB entries will not be used for any legitimate subsequent page table walks. I have some minor changes which I'll send as v5 based on kernel/git/arm64/linux.git for-next/core. Thanks, Cov -- Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.