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[2003:cb:c739:8e00:7a46:1b8c:8b13:d3d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432d550c072sm189445e9.29.2024.11.12.13.35.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Nov 2024 13:35:44 -0800 (PST) Message-ID: Date: Tue, 12 Nov 2024 22:35:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/7] accel/kvm: Keep track of the HWPoisonPage page_size To: William Roche , kvm@vger.kernel.org, qemu-devel@nongnu.org, qemu-arm@nongnu.org Cc: peterx@redhat.com, pbonzini@redhat.com, richard.henderson@linaro.org, philmd@linaro.org, peter.maydell@linaro.org, mtosatti@redhat.com, imammedo@redhat.com, eduardo@habkost.net, marcel.apfelbaum@gmail.com, wangyanan55@huawei.com, zhao1.liu@intel.com, joao.m.martins@oracle.com References: <20241107102126.2183152-1-william.roche@oracle.com> <20241107102126.2183152-2-william.roche@oracle.com> <1f59ca33-4861-406e-9490-af3e4df08efc@oracle.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; 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=-0.122, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.671, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 12.11.24 19:17, William Roche wrote: > On 11/12/24 11:30, David Hildenbrand wrote: >> On 07.11.24 11:21, “William Roche wrote: >>> From: William Roche >>> >>> When a memory page is added to the hwpoison_page_list, include >>> the page size information.  This size is the backend real page >>> size. To better deal with hugepages, we create a single entry >>> for the entire page. >>> >>> Signed-off-by: William Roche >>> --- >>>   accel/kvm/kvm-all.c       |  8 +++++++- >>>   include/exec/cpu-common.h |  1 + >>>   system/physmem.c          | 13 +++++++++++++ >>>   3 files changed, 21 insertions(+), 1 deletion(-) >>> >>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c >>> index 801cff16a5..6dd06f5edf 100644 >>> --- a/accel/kvm/kvm-all.c >>> +++ b/accel/kvm/kvm-all.c >>> @@ -1266,6 +1266,7 @@ int kvm_vm_check_extension(KVMState *s, unsigned >>> int extension) >>>    */ >>>   typedef struct HWPoisonPage { >>>       ram_addr_t ram_addr; >>> +    size_t     page_size; >>>       QLIST_ENTRY(HWPoisonPage) list; >>>   } HWPoisonPage; >>> @@ -1278,7 +1279,7 @@ static void kvm_unpoison_all(void *param) >>>       QLIST_FOREACH_SAFE(page, &hwpoison_page_list, list, next_page) { >>>           QLIST_REMOVE(page, list); >>> -        qemu_ram_remap(page->ram_addr, TARGET_PAGE_SIZE); >>> +        qemu_ram_remap(page->ram_addr, page->page_size); >>>           g_free(page); >> >> I'm curious, can't we simply drop the size parameter from qemu_ram_remap() >> completely and determine the page size internally from the RAMBlock that >> we are looking up already? >> >> This way, we avoid yet another lookup in qemu_ram_pagesize_from_addr(), >> and can just handle it completely in qemu_ram_remap(). >> >> In particular, to be future proof, we should also align the offset down to >> the pagesize. >> >> I'm thinking about something like this: >> >> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c >> index 801cff16a5..8a47aa7258 100644 >> --- a/accel/kvm/kvm-all.c >> +++ b/accel/kvm/kvm-all.c >> @@ -1278,7 +1278,7 @@ static void kvm_unpoison_all(void *param) >> >>      QLIST_FOREACH_SAFE(page, &hwpoison_page_list, list, next_page) { >>          QLIST_REMOVE(page, list); >> -        qemu_ram_remap(page->ram_addr, TARGET_PAGE_SIZE); >> +        qemu_ram_remap(page->ram_addr); >>          g_free(page); >>      } >>  } >> diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h >> index 638dc806a5..50a829d31f 100644 >> --- a/include/exec/cpu-common.h >> +++ b/include/exec/cpu-common.h >> @@ -67,7 +67,7 @@ typedef uintptr_t ram_addr_t; >> >>  /* memory API */ >> >> -void qemu_ram_remap(ram_addr_t addr, ram_addr_t length); >> +void qemu_ram_remap(ram_addr_t addr); >>  /* This should not be used by devices.  */ >>  ram_addr_t qemu_ram_addr_from_host(void *ptr); >>  ram_addr_t qemu_ram_addr_from_host_nofail(void *ptr); >> diff --git a/system/physmem.c b/system/physmem.c >> index dc1db3a384..5f19bec089 100644 >> --- a/system/physmem.c >> +++ b/system/physmem.c >> @@ -2167,10 +2167,10 @@ void qemu_ram_free(RAMBlock *block) >>  } >> >>  #ifndef _WIN32 >> -void qemu_ram_remap(ram_addr_t addr, ram_addr_t length) >> +void qemu_ram_remap(ram_addr_t addr) >>  { >>      RAMBlock *block; >> -    ram_addr_t offset; >> +    ram_addr_t offset, length; >>      int flags; >>      void *area, *vaddr; >>      int prot; >> @@ -2178,6 +2178,10 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t >> length) >>      RAMBLOCK_FOREACH(block) { >>          offset = addr - block->offset; >>          if (offset < block->max_length) { >> +            /* Respect the pagesize of our RAMBlock. */ >> +            offset = QEMU_ALIGN_DOWN(offset, qemu_ram_pagesize(block)); >> +            length = qemu_ram_pagesize(block); >> + >>              vaddr = ramblock_ptr(block, offset); >>              if (block->flags & RAM_PREALLOC) { >>                  ; >> @@ -2206,6 +2210,8 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t >> length) >>                  memory_try_enable_merging(vaddr, length); >>                  qemu_ram_setup_dump(vaddr, length); >>              } >> + >> +            break; >>          } >>      } >>  } >> >> > > > Yes this is a working possibility, and as you say it would provide the > advantage to avoid a size lookup (needed because the kernel siginfo can > be incorrect) and avoid tracking the poisoned pages size, with the > addresses. > > But if we want to keep the information about the loss of a large page > (which I think is useful) we would have to introduce the page size > lookup when adding the page to the poison list. So according to me, Right, that would be independent of the remap logic. What I dislike about qemu_ram_remap() is that it looks like we could be remapping a range that's possibly larger than a single page. But it really only works on a single address, expanding that to the page. Passing in a length that crosses RAMBlocks would not work as expected ... So I'd prefer if we let qemu_ram_remap() do exactly that ... remap a single page ... > keeping track of the page size and reusing it on remap isn't so bad. But > if you prefer that we don't track the page size and do a lookup on page > insert into the poison list and another in qemu_ram_remap(), of course > we can do that. ... and lookup the page size manually here if we really have to, for example to warn/trace errors. > > There is also something to consider about the future: we'll also have to > deal with migration of VM that have been impacted by a memory error. And > knowing about the poisoned pages size could be useful too. But this is > another topic... Yes, although the destination should be able to derive the same thing from the address I guess. We expect src and dst QEMU to use the same memory backing. -- Cheers, David / dhildenb