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AJvYcCWnZgJwC7F9BuhKgnzLG/i1R3J66CqRUL6CSErox4ZxXS9XOICcjlVUXLVGeQQAF+KN2FbimUKsSg==@kvack.org X-Gm-Message-State: AOJu0YzcNANUMvOQT2EtOZVBcKGymo2LM6yEu6LsWkFjYyORls3AOLz2 hq2XCSvNfO3EEVJ1Y3aMWAWs7+uABGcBUXisNX0HYwnIAdcJNnpaCaLlGEMitrPPMBJRsmz+3wD HY7iR34T2WIsqQTLBSeB71D8KIA== X-Google-Smtp-Source: AGHT+IGZsqgq2G2XIkR7qcIy/VW6gTpaWqSm/97lo1vVmXSkPBk6jSv3JCyUAX+95O4wmkeQ/wPnsUapN2qJLw24ag== X-Received: from plnq12.prod.google.com ([2002:a17:902:f78c:b0:223:5693:a4e9]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:2ec8:b0:224:1943:c65 with SMTP id d9443c01a7336-231d44e64e6mr60539585ad.14.1747427620934; Fri, 16 May 2025 13:33:40 -0700 (PDT) Date: Fri, 16 May 2025 13:33:39 -0700 In-Reply-To: (message from Ackerley Tng on Fri, 16 May 2025 07:07:27 -0700) Mime-Version: 1.0 Message-ID: Subject: Re: [RFC PATCH v2 29/51] mm: guestmem_hugetlb: Wrap HugeTLB as an allocator for guest_memfd From: Ackerley Tng To: Ackerley Tng Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, aik@amd.com, ajones@ventanamicro.com, akpm@linux-foundation.org, amoorthy@google.com, anthony.yznaga@oracle.com, anup@brainfault.org, aou@eecs.berkeley.edu, bfoster@redhat.com, binbin.wu@linux.intel.com, brauner@kernel.org, catalin.marinas@arm.com, chao.p.peng@intel.com, chenhuacai@kernel.org, dave.hansen@intel.com, david@redhat.com, dmatlack@google.com, dwmw@amazon.co.uk, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, graf@amazon.com, haibo1.xu@intel.com, hch@infradead.org, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, kirill.shutemov@intel.com, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maz@kernel.org, mic@digikod.net, michael.roth@amd.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, pdurrant@amazon.co.uk, peterx@redhat.com, pgonda@google.com, pvorel@suse.cz, qperret@google.com, quic_cvanscha@quicinc.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, quic_svaddagi@quicinc.com, quic_tsoni@quicinc.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, tabba@google.com, thomas.lendacky@amd.com, usama.arif@bytedance.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: 6iyyes3w7wao9dyy36ddc3h8ccc1x9et X-Rspam-User: X-Rspamd-Queue-Id: 43A20C0014 X-Rspamd-Server: rspam06 X-HE-Tag: 1747427622-213560 X-HE-Meta: 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 PfepaB5c 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Ackerley Tng writes: > Ackerley Tng writes: > >> guestmem_hugetlb is an allocator for guest_memfd. It wraps HugeTLB to >> provide huge folios for guest_memfd. >> >> This patch also introduces guestmem_allocator_operations as a set of >> operations that allocators for guest_memfd can provide. In a later >> patch, guest_memfd will use these operations to manage pages from an >> allocator. >> >> The allocator operations are memory-management specific and are placed >> in mm/ so key mm-specific functions do not have to be exposed >> unnecessarily. >> >> Signed-off-by: Ackerley Tng >> >> Change-Id: I3cafe111ea7b3c84755d7112ff8f8c541c11136d >> --- >> include/linux/guestmem.h | 20 +++++ >> include/uapi/linux/guestmem.h | 29 +++++++ >> mm/Kconfig | 5 +- >> mm/guestmem_hugetlb.c | 159 ++++++++++++++++++++++++++++++++++ >> 4 files changed, 212 insertions(+), 1 deletion(-) >> create mode 100644 include/linux/guestmem.h >> create mode 100644 include/uapi/linux/guestmem.h >> >> >> >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 131adc49f58d..bb6e39e37245 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -1218,7 +1218,10 @@ config SECRETMEM >> >> config GUESTMEM_HUGETLB >> bool "Enable guestmem_hugetlb allocator for guest_memfd" >> - depends on HUGETLBFS >> + select GUESTMEM >> + select HUGETLBFS >> + select HUGETLB_PAGE >> + select HUGETLB_PAGE_OPTIMIZE_VMEMMAP > > My bad. I left out CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y in > my testing and just found that when it is set, I hit > > BUG_ON(pte_page(ptep_get(pte)) != walk->reuse_page); > > with the basic guest_memfd_test on splitting pages on allocation. > > I'll follow up with the fix soon. > > Another note about testing: I've been testing in a nested VM for the > development process: > > 1. Host > 2. VM for development > 3. Nested VM running kernel being developed > 4. Nested nested VMs created during selftests > > This series has not yet been tested on a physical host. > >> help >> Enable this to make HugeTLB folios available to guest_memfd >> (KVM virtualization) as backing memory. >> >> >> Here's the fix for this issue >From 998af6404d4e39920ba42764e7f3815cb9bb9e3d Mon Sep 17 00:00:00 2001 Message-ID: <998af6404d4e39920ba42764e7f3815cb9bb9e3d.1747427489.git.ackerleytng@google.com> From: Ackerley Tng Date: Fri, 16 May 2025 13:14:55 -0700 Subject: [RFC PATCH v2 1/1] KVM: guest_memfd: Reorder undoing vmemmap optimization and stashing hugetlb folio metadata Without this patch, when HugeTLB folio metadata is stashed, the vmemmap_optimized flag, stored in a HugeTLB folio's folio->private was stashed as set. The first splitting works, but on merging, when the folio metadata was unstashed, vmemmap_optimized is unstashed as set, making the call to hugetlb_vmemmap_optimize_folio() skip actually applying optimizations. On a second split, hugetlb_vmemmap_restore_folio() attempts to reapply optimizations when it was already applied, hence hitting the BUG(). Signed-off-by: Ackerley Tng --- mm/guestmem_hugetlb.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/mm/guestmem_hugetlb.c b/mm/guestmem_hugetlb.c index 8727598cf18e..2c0192543676 100644 --- a/mm/guestmem_hugetlb.c +++ b/mm/guestmem_hugetlb.c @@ -200,16 +200,21 @@ static int guestmem_hugetlb_split_folio(struct folio *folio) return 0; orig_nr_pages = folio_nr_pages(folio); - ret = guestmem_hugetlb_stash_metadata(folio); + + /* + * hugetlb_vmemmap_restore_folio() has to be called ahead of the rest + * because it checks page type. This doesn't actually split the folio, + * so the first few struct pages are still intact. + */ + ret = hugetlb_vmemmap_restore_folio(folio_hstate(folio), folio); if (ret) return ret; /* - * hugetlb_vmemmap_restore_folio() has to be called ahead of the rest - * because it checks and page type. This doesn't actually split the - * folio, so the first few struct pages are still intact. + * Stash metadata after vmemmap stuff so the outcome of the vmemmap + * restoration is stashed. */ - ret = hugetlb_vmemmap_restore_folio(folio_hstate(folio), folio); + ret = guestmem_hugetlb_stash_metadata(folio); if (ret) goto err; @@ -254,8 +259,7 @@ static int guestmem_hugetlb_split_folio(struct folio *folio) return 0; err: - guestmem_hugetlb_unstash_free_metadata(folio); - + hugetlb_vmemmap_optimize_folio(folio_hstate(folio), folio); return ret; } -- 2.49.0.1101.gccaa498523-goog