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Shutemov" , Mahesh J Salgaonkar , Michael Ellerman , Madhavan Srinivasan , "Aneesh Kumar K . V" , Donet Tom , LKML , Sachin P Bappalige Subject: Re: [RFC 1/2] cma: Fix CMA_MIN_ALIGNMENT_BYTES during early_init In-Reply-To: <83eb128e-4f06-4725-a843-a4563f246a44@redhat.com> Date: Thu, 10 Oct 2024 08:49:20 +0530 Message-ID: <871q0ofxvr.fsf@gmail.com> References: <83eb128e-4f06-4725-a843-a4563f246a44@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: David Hildenbrand writes: > On 08.10.24 15:27, Ritesh Harjani (IBM) wrote: >> During early init CMA_MIN_ALIGNMENT_BYTES can be PAGE_SIZE, >> since pageblock_order is still zero and it gets initialized >> later during paging_init() e.g. >> paging_init() -> free_area_init() -> set_pageblock_order(). >> >> One such use case is - >> early_setup() -> early_init_devtree() -> fadump_reserve_mem() >> >> This causes CMA memory alignment check to be bypassed in >> cma_init_reserved_mem(). Then later cma_activate_area() can hit >> a VM_BUG_ON_PAGE(pfn & ((1 << order) - 1)) if the reserved memory >> area was not pageblock_order aligned. >> >> Instead of fixing it locally for fadump case on PowerPC, I believe >> this should be fixed for CMA_MIN_ALIGNMENT_BYTES. > > I think we should add a way to catch the usage of > CMA_MIN_ALIGNMENT_BYTES before it actually has meaning (before > pageblock_order was set) Maybe by enforcing that the pageblock_order should not be zero where we do the alignment check then? i.e. in cma_init_reserved_mem() diff --git a/mm/cma.c b/mm/cma.c index 3e9724716bad..36d753e7a0bf 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -182,6 +182,15 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size, if (!size || !memblock_is_region_reserved(base, size)) return -EINVAL; + /* + * CMA uses CMA_MIN_ALIGNMENT_BYTES as alignment requirement which + * needs pageblock_order to be initialized. Let's enforce it. + */ + if (!pageblock_order) { + pr_err("pageblock_order not yet initialized. Called during early boot?\n"); + return -EINVAL; + } + /* ensure minimal alignment required by mm core */ if (!IS_ALIGNED(base | size, CMA_MIN_ALIGNMENT_BYTES)) return -EINVAL; > and fix the PowerPC usage by reshuffling the > code accordingly. Ok. I will submit a v2 with the above patch incldued. Thanks for the review! -ritesh