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Wed, 06 May 2026 11:28:24 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 6 May 2026 20:28:23 +0200 To: shivamkalra98@zohomail.in Cc: Andrew Morton , Uladzislau Rezki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alice Ryhl , Danilo Krummrich Subject: Re: [PATCH v12 3/5] mm/vmalloc: use physical page count in vread_iter() Message-ID: References: <20260428-vmalloc-shrink-v12-0-3c18c9172eb1@zohomail.in> <20260428-vmalloc-shrink-v12-3-3c18c9172eb1@zohomail.in> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260428-vmalloc-shrink-v12-3-3c18c9172eb1@zohomail.in> On Tue, Apr 28, 2026 at 01:54:18AM +0530, Shivam Kalra via B4 Relay wrote: > From: Shivam Kalra > > Update vread_iter() to derive the vm area size from vm->nr_pages rather > than get_vm_area_size(). > > Currently both values are equivalent, but the upcoming vrealloc() shrink > functionality will free pages without reducing the virtual reservation > size. After such a shrink, the old get_vm_area_size() based calculation > would overestimate the mapped range, causing vread_iter() to attempt > reading from unmapped addresses. Switch to vm->nr_pages now so the > reader remains correct once shrink support is added. > > Signed-off-by: Shivam Kalra > --- > mm/vmalloc.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 9cb3e287a1e8..65e0a23efb3b 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -4661,7 +4661,14 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count) > smp_rmb(); > > vaddr = (char *) va->va_start; > - size = vm ? get_vm_area_size(vm) : va_size(va); > + if (vm) > + /* > + * Cannot use get_vm_area_size() because realloc() > + * may shrink the mapping and area->size may be outdated. > + */ > + size = vm->nr_pages << PAGE_SHIFT; > + else > + size = va_size(va); > > if (addr >= vaddr + size) > goto next_va; > > -- > 2.43.0 > > Reviewed-by: Uladzislau Rezki (Sony) -- Uladzislau Rezki