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(Postfix) with ESMTPSA id 176CD6091B256 for ; Mon, 25 May 2020 17:51:33 +0200 (CEST) To: "xen-devel@lists.xenproject.org" From: Hans van Kranenburg Subject: Bug: toolstack allows too low values to be set for shadow_memory Autocrypt: addr=hans@knorrie.org; keydata= mQINBFo2pooBEADwTBe/lrCa78zuhVkmpvuN+pXPWHkYs0LuAgJrOsOKhxLkYXn6Pn7e3xm+ ySfxwtFmqLUMPWujQYF0r5C6DteypL7XvkPP+FPVlQnDIifyEoKq8JZRPsAFt1S87QThYPC3 mjfluLUKVBP21H3ZFUGjcf+hnJSN9d9MuSQmAvtJiLbRTo5DTZZvO/SuQlmafaEQteaOswme DKRcIYj7+FokaW9n90P8agvPZJn50MCKy1D2QZwvw0g2ZMR8yUdtsX6fHTe7Ym+tHIYM3Tsg 2KKgt17NTxIqyttcAIaVRs4+dnQ23J98iFmVHyT+X2Jou+KpHuULES8562QltmkchA7YxZpT mLMZ6TPit+sIocvxFE5dGiT1FMpjM5mOVCNOP+KOup/N7jobCG15haKWtu9k0kPz+trT3NOn gZXecYzBmasSJro60O4bwBayG9ILHNn+v/ZLg/jv33X2MV7oYXf+ustwjXnYUqVmjZkdI/pt 30lcNUxCANvTF861OgvZUR4WoMNK4krXtodBoEImjmT385LATGFt9HnXd1rQ4QzqyMPBk84j roX5NpOzNZrNJiUxj+aUQZcINtbpmvskGpJX0RsfhOh2fxfQ39ZP/0a2C59gBQuVCH6C5qsY rc1qTIpGdPYT+J1S2rY88AvPpr2JHZbiVqeB3jIlwVSmkYeB/QARAQABtCZIYW5zIHZhbiBL 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text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" This bug report is a follow-up to the thread "Domu windows 2012 crash" on the xen-users list. In there we found out that it is possible to set a value for shadow_memory that is lower than a safe minimum value. This became apparent after XSA-304, which caused using more of this type of memory. Having a hardcoded line like shadow_memory = 8 results in random crashes of the guest, with the following errors in xl dmesg of the host: (XEN) Failed to shatter gfn 105245: -12 (XEN) d75v1 EPT violation 0x19c (--x/rw-) gpa 0x00000105245760 mfn 0x285245 type 0 (XEN) d75v1 Walking EPT tables for GFN 105245: (XEN) d75v1 epte 9c000004105f9007 (XEN) d75v1 epte 9c000002800000f3 (XEN) d75v1 --- GLA 0x7ff98b40d760 (XEN) domain_crash called from vmx.c:3497 (XEN) Domain 75 (vcpu#1) crashed on cpu#4: (XEN) ----[ Xen-4.11.4-pre x86_64 debug=n Not tainted ]---- (XEN) CPU: 4 (XEN) RIP: 0033:[<00007ff98b40d760>] (XEN) RFLAGS: 0000000000010216 CONTEXT: hvm guest (d75v1) (XEN) rax: 0000000000001212 rbx: 000000c714d9da58 rcx: 0000023500001590 (XEN) rdx: 000000c700000001 rsi: 000000c714d9da18 rdi: 000000c714d9db20 (XEN) rbp: 000000c714d9d950 rsp: 000000c714d9d918 r8: 0000023500001470 (XEN) r9: 00000235000014f0 r10: 00007ff99c5c0923 r11: 000000c714d9d970 (XEN) r12: 0000000000000000 r13: 000000c714d9d9d0 r14: 000000c714d9da58 (XEN) r15: 0000000000000006 cr0: 0000000080050031 cr4: 0000000000060678 (XEN) cr3: 00000001d9458002 cr2: 00007ff98b6fa048 (XEN) fsb: 0000000000000000 gsb: 000000c714e9e000 gss: ffffcd015dc40000 (XEN) ds: 002b es: 002b fs: 0053 gs: 002b ss: 002b cs: 0033 Why do users have this shadow_memory line in their guest config file? Well, I guess it's simply because there are not many proper examples of how to run Windows under Xen, so whoever is searching ze interwobz for it will end up on a page like... https://www.howtoforge.com/how-to-run-fully-virtualized-guests-hvm-with-xen-3.2-on-debian-lenny-x86_64 ...and then start copy pasting and adjusting until things work. Or... already have such a config for 10+ years and just only adjust things when it breaks after upgrading Xen. Hans van Kranenburg