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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sFJe1ZuJ+f8GRxdAgY8srN1RiSC4v2YvCNlLlmUtqGq0JnBUN5kBgYHgAdtl1+WBE 86jkDS1YRlLddNDdfgMKb3RVjJvd/DDlHtSCIqjgjuwU2N63jNz2qDHOX98sxoLboM FHd7s/Mzcrg9P/Q3NGrRDdX07qr9iwtrz3o25+oI= Date: Wed, 19 Aug 2026 11:11:09 +0100 From: Catalin Marinas To: James Houghton Cc: Will Deacon , Muchun Song , Oscar Salvador , Nikos Nikoleris , Linu Cherian , Mark Rutland , David Hildenbrand , Andrew Morton , Ryan Roberts , Nanyong Sun , Yu Zhao , Frank van der Linden , David Rientjes , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH 17/18] arm64: Permit onlining of HVO-incompatible late CPUs if HVO is not in use Message-ID: References: <20260708031129.3503195-1-jthoughton@google.com> <20260708031129.3503195-18-jthoughton@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260708031129.3503195-18-jthoughton@google.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 146F0A000C X-Stat-Signature: w8pgfz1oz9gtcyos55o7icrwfz54wfom X-Rspam-User: X-HE-Tag: 1787134275-451221 X-HE-Meta: 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 boNhDQqf BD3UpVZ+kK7PpnMArr6JmLVnYe5xbzFYwO4FX1cTirbzqK/Mq/u8771lRujfAPA0avT4jT7lXeQFiGVWrOBhTMUAdbnLOeZTuhUfTMwIgSA/bjKz+9YuoYD6/0uyBTLALjXdocO8h+a0dontGmEsnAzrPBLhoD93TpdCjsoJUueZ/i1FU5LsIq7KIKMpORvjNcqIt/XMsXvEyeJz1Ui1LbX2D3BkFTxytFTFDdTOJQB0N7bs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 08, 2026 at 03:11:27AM +0000, James Houghton wrote: > First, HVO must have ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU so that > incompatible CPUs can be onlined if HVO is not in use. The > late_cpu_enable() callback is used to check if HVO is truly in use. > > If the late CPU is incompatible with HVO and HVO is *not* in use, HVO > becomes permanently disabled. > > If the late CPU is incompatible with HVO and HVO *is* in use, the CPU > is not onlined. I haven't looked in detail at the logic here but do we actually care about this? We still need to solve the BBML2 requirement around patches 12 and 13. BBML2 won't be an optionally late feature for other reasons, so such CPUs won't be allowed. This leaves us with HW AF. In mainline, the check is done on the sanitised regs but IIRC these can still be overridden on late CPU onlining with a warning. We only use this check as an optimisation, so not an issue in mainline but can be come problematic with HVO. If we don't have a strong use-case for mismatched HAFDBS support, I'd drop these last patches for now. -- Catalin