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[91.12.103.116]) by smtp.gmail.com with ESMTPSA id x7sm5111331wrq.69.2021.10.13.00.14.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Oct 2021 00:14:36 -0700 (PDT) Subject: Re: [PATCH v1 2/2] memory: Update description of memory_region_is_mapped() From: David Hildenbrand To: Igor Mammedov References: <20211011174522.14351-1-david@redhat.com> <20211011174522.14351-3-david@redhat.com> <93dead18-5ea5-0afe-18c1-de9a06773687@linaro.org> <8108c69d-a596-d6c9-a116-783f47904deb@amsat.org> <845d3d5f-f9e9-d59d-c868-5a9825eb7fba@redhat.com> <20211012105300.1ef25440@redhat.com> <20211012120059.14e19dc1@redhat.com> <84adb9d1-6e30-7d5e-a362-0a81ea4b8b01@redhat.com> Organization: Red Hat Message-ID: <067a10ee-0897-df8d-2eff-b347c5958b03@redhat.com> Date: Wed, 13 Oct 2021 09:14:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <84adb9d1-6e30-7d5e-a362-0a81ea4b8b01@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.049, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , Richard Henderson , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Peter Xu , qemu-devel@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 12.10.21 12:09, David Hildenbrand wrote: >> >> The less confusing would be one where check works for any memory region >> involved. > > Exactly, so for any alias, even in-between another alias and the target. > >> >>>> >>>> >>>>> I am not aware of actual issues, this is rather a cleanup. >>>>> >>>>> Signed-off-by: David Hildenbrand >>>>> >>>>> diff --git a/include/exec/memory.h b/include/exec/memory.h >>>>> index 75b4f600e3..93d0190202 100644 >>>>> --- a/include/exec/memory.h >>>>> +++ b/include/exec/memory.h >>>>> @@ -728,6 +728,7 @@ struct MemoryRegion { >>>>> const MemoryRegionOps *ops; >>>>> void *opaque; >>>>> MemoryRegion *container; >>>>> + int mapped_via_alias; /* Mapped via an alias, container might be NULL */ >>>>> Int128 size; >>>>> hwaddr addr; >>>>> void (*destructor)(MemoryRegion *mr); >>>>> diff --git a/softmmu/memory.c b/softmmu/memory.c >>>>> index 3bcfc3899b..1168a00819 100644 >>>>> --- a/softmmu/memory.c >>>>> +++ b/softmmu/memory.c >>>>> @@ -2535,8 +2535,13 @@ static void memory_region_add_subregion_common(MemoryRegion *mr, >>>>> hwaddr offset, >>>>> MemoryRegion *subregion) >>>>> { >>>>> + MemoryRegion *alias; >>>>> + >>>>> assert(!subregion->container); >>>>> subregion->container = mr; >>>>> + for (alias = subregion->alias; alias; alias = alias->alias) { >>>>> + alias->mapped_via_alias++; >>>> >>>> it it necessary to update mapped_via_alias for intermediate aliases? >>>> Why not just update on counter only on leaf (aliased region)? >>> >>> Assume we have alias0 -> alias1 -> region and map alias0. >>> >>> Once alias0 is mapped it will have ->container set and >>> memory_region_is_mapped(alias0) will return "true". >>> >>> With my patch, both, "alias1" and the region will be marked >>> "mapped_via_alias" and memory_region_is_mapped() will succeed on both of >>> them. With what you propose, memory_region_is_mapped() would only >>> succeed on the region (well, and on alias 0) but not on alias1. >> >> as long as add_subregion increments counter on leaf it doesn't matter >> how many intermediate aliases are there. Check on every one of them >> should end up at the leaf counter (at expense of traversing >> chain on every check but less state to track/think about). >> > > Sure, we could also let memory_region_is_mapped() walk all aliases to > the leaf. Not sure though, if it really simplifies things. It merely > adds another loop and doesn't get rid of the others :) But I don't > particularly care. > I just realized that this might not be what we want: we could get false positives when a memory region is referenced via multiple alias and only one of them is mapped. memory_region_is_mapped() could return "true" for an alias that isn't actually mapped. -- Thanks, David / dhildenb