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b=FTRgX+Q/6LPx/bvDmDU2kJ8GmAsSNZui+PwVv4w61rL39dDN+2G4enh2VmRozbYn7 GsJbcHWY2ijfeq1hNqCZi/+5CZNATEMUGN+NGRIQQnZn98SGbEuaON+JGNeIPrSQn5 86T3bIan+pShYe5kWz5wOKhgF1CL11s0XSD0NDhY4U1chBowSHfKcbIRmGV028Blt9 D4EmmcMcsX2VpqRWA55TOBkh21SUAIw0ENDA/MKBMTJkU5ecuzoQEtRHTQyWcp3Cv0 yvm+vszfZbuMimHyJy2OiLJL2e04N4YrpSkkGy/laeVYd9BQVybLMKHZC/IsISTNXD r4+/mJDA/Wp9A== Date: Fri, 31 Jul 2026 08:21:05 +0300 From: Mike Rapoport To: Yosry Ahmed Cc: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Vlastimil Babka , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, Sumit Garg , Will Deacon , rientjes@google.com, "Kalyazin, Nikita" , patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Patrick Bellasi , Reiji Watanabe , Sean Christopherson , Nikita Kalyazin Subject: Re: [PATCH v3 01/26] set_memory: add folio_{zap,restore}_direct_map helpers Message-ID: References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-1-6f5729aa9832@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 5F59840005 X-Stat-Signature: 9dy4kn87nryh4yxofsqxmps5gsd7p7xi X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1785475279-512420 X-HE-Meta: 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 FAmeITfW e+qS4+2si4BdYkqoKlpaHibNHCSvF3a3McpE6RHH1GTznbaFrmHEUtnlrMGG6dMSRILSy8BgE0wukt0rkkC4gsxxaUZNY8tb/FIDBbZx0FUFtY5UMcyn25wAnJO8IupotRKJe46aJ7Cnc4FORukFZkoQ4mWeAaS/OdgB1YE0+x7KkpAoZufamhQsaGFUF+G3UTLHpRkc56G0BstZNqM//BgyqXpAKZ73sfsHHv6X0UlLZGy6DabhO9oA92t2HLUmHry+/jXs2i9ocbzmyEsdznldRyxQlR8ez72wyhzZIaXWAFAHjBpC2+98jmUM7TIl5j3lcoSwHtrmL+UCVr46vaVX0iM7zoxSThUG2 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 30, 2026 at 08:34:57PM +0000, Yosry Ahmed wrote: > On Sun, Jul 26, 2026 at 10:22:34PM +0000, Brendan Jackman wrote: > > From: Nikita Kalyazin > > > > Let's provide folio_{zap,restore}_direct_map helpers as preparation for > > supporting removal of the direct map for guest_memfd folios. > > In folio_zap_direct_map(), flush TLB to make sure the data is not > > accessible. On some architectures, there may be a double TLB flush > > issued because set_direct_map_valid_noflush already performs a flush > > internally. > > > > The new helpers need to be accessible to KVM on architectures that > > support guest_memfd (x86 and arm64). > > > > Direct map removal gives guest_memfd the same protection that > > memfd_secret does, such as hardening against Spectre-like attacks > > through in-kernel gadgets. > > > > Acked-by: David Hildenbrand (Arm) > > Signed-off-by: Nikita Kalyazin > > [Added comment, dropped modified set_direct_map API, added highmem check] > > Signed-off-by: Brendan Jackman > > --- > > include/linux/set_memory.h | 13 +++++++++++++ > > mm/memory.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++ > > 2 files changed, 59 insertions(+) > > > > diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h > > index 3030d9245f5ac..1bf2a15bca118 100644 > > --- a/include/linux/set_memory.h > > +++ b/include/linux/set_memory.h > > @@ -40,6 +40,15 @@ static inline int set_direct_map_valid_noflush(struct page *page, > > return 0; > > } > > > > +static inline int folio_zap_direct_map(struct folio *folio) > > +{ > > + return 0; > > Should this return an error (e.g. -EOPNOTSUPP)? Seems like it would > silently succeed if the arch doesn't actually support removing from the > direct map. That's the pattern we have now for all set_memory APIs. -- Sincerely yours, Mike.