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b=k9Zp8zfa1ZmOgIw9AvsC0jJ3gGh7VbtLISPNsLrxUqcsBAt9qAuUDY11NK7V0XtTL h3Ada4S50vzVNffn6XMcfann7GJH40vy0tUzoYh9/Q0hc1XuFft1lwOyrAz0W3/2ez C8YPfSzIH0/gzCO5xnHwiICmh2+S/CWP7o69hrz1Xq60SGt4Kek2E2c+40pyotrWLn L++RQ00DlNYtkSMHuABLS1PpMjnlpEwYMjRfAZk75De9n6gifR4xMwwbdx+vY9WgAc xUm597feIzpmo2R7FjKGr8XSpjHqr+S29XtVhlzhif62yJiSHNT+PkiQ54pbf+q5tO 3Vkaj6f2LfI1w== Date: Thu, 30 Jul 2026 20:34:57 +0000 From: Yosry Ahmed To: Brendan Jackman Cc: Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Vlastimil Babka , Mike Rapoport , 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: <20260726-page_alloc-unmapped-v3-1-6f5729aa9832@google.com> X-Stat-Signature: 5ri7w9oyqsza6qdaq1zpx5664cmhzf8q X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 9E8D7C0009 X-HE-Tag: 1785443701-733606 X-HE-Meta: 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 8cEm2rXW a6f5nLvp4ohyAEtyxuIPRjkKVuHje0lmLU2URpnKIxP7n0h6K8BDzDqIpZ7/xb67yhy7OXcqcgVlmShje+fGG5byFvSMnnaz2H3bay+U4HU79zVdNvdzu70kC7picAsXCLUs4XKZRHIiUbZNMOS7lgPAyQk0c29P4XMOD4XRtDpQo9OzCEGfVqEGMJLgJW+PB4zMSlYtxsexagJDegSpkRNKeiiUHSg3EjqEy8Z3YJDKAj0TYZYJtQBYf2SIpAh6oHDza+FPpaCCgpDqtqYdphx1cYVRqF9mKwjLj/5n2IORkPZ7kpi2Aw2otCVCsupGkSXJgjhHom3AP2HMd/1TejGorQA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.