@rafael - One more question about Stepping 5/6. I have formerly read your explanation that stepping 6 would be required to be able to enable arch_capabilities. And we planned to add all SRUs with stepping 6 right away and keep the Delta to consider all versions to be stepping 6.
But then I have seen [1] and in particular [2]. Overall this adds more complexity but also more ability to CPU model definitions. But in between the lines in [2] I read that arch_capabilities gets enabled by default and stepping goes back to 5. That seems to imply that enabling it on stepping 5 isn't an issue. If it does work doing the SRU that way it will ease maintenance in the future. Especially since these versioned types will make maintaining Delta in that area even more complex. And it would avoid the upgrade issue on Disco where the CascadeLake would change. Therefore I wondered if we could make the backport use stepping 5 which would allow to not carry the delta forever in >=Eoan. Could you make a PPA build as it is right now, but with stepping 5 and check if using arch_capabilities still works for you? [1]: https://www.mail-archive.com/qemu-devel@nongnu.org/msg626545.html [2]: https://www.mail-archive.com/qemu-devel@nongnu.org/msg626550.html -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1828495 Title: [KVM][CLX] CPUID_7_0_EDX_ARCH_CAPABILITIES is not enabled in VM. Status in intel: New Status in linux package in Ubuntu: Confirmed Status in qemu package in Ubuntu: Confirmed Status in linux source package in Bionic: New Status in qemu source package in Bionic: Confirmed Status in linux source package in Cosmic: New Status in qemu source package in Cosmic: Confirmed Status in linux source package in Disco: New Status in qemu source package in Disco: Confirmed Status in linux source package in Eoan: Confirmed Status in qemu source package in Eoan: Confirmed Bug description: [Impact] * QEMU does not support IceLake and CascadeLake CPUs specific features. * Most important feature to be supported is: IA32_ARCH_CAPABILITIES MSR. * With IA32_ARCH_CAPABILITIES, QEMU is able to advertise HW mitigations: - Rogue Data Cache Load - Enhanced IBRS - RSB Alternate - L1D flush need on VMENTRY - speculative Store Bypass to guests, as described in document: Intel 336996-Speculative-Execution-Side-Channel-Mitigations.pdf [Test Case] * From Original Description: """ 1. Boot up guest using: -cpu Cascadelake-Server [root@clx-2s2 yexin]# qemu-system-x86_64 -accel kvm -drive if=virtio,id=hd,file=/home/x/x,format=qcow2 -m 4096 -smp 4 -cpu Cascadelake-Server -serial stdio char device redirected to /dev/pts/3 (label serial0) qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:ECX [bit 4] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:ECX [bit 4] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:ECX [bit 4] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:ECX [bit 4] 2. To check CPU ID related to features[FEAT_7_0_EDX] ：CPUID_7_0_EDX_ARCH_CAPABILITIES Expected Result: Both host and guest's CPUID.07H EDX bit 29 should be 1. Actual Result: Host's cpuid: 0x00000007 0x00: eax=0x00000000 ebx=0xd39ffffb ecx=0x00000818 edx=0xbc000000 (EDX bit 29=1) Guest's cpuid : 0x00000007 0x00: eax=0x00000000 ebx=0xd19f0fb9 ecx=0x00000818 edx=0x84000000 (EDX bit 29=0) Commit:2bdb76c015df7125783d8394d6339d181cb5bc30 Target Kerned: 5.1 Target Release: 19.10 """ [Regression Potential] * Most changes are related to CPU type definitions and its supported features. They are all based in upstream changes but, for obvious reasons, backporting and/or cherry-picking those could bring issues. Biggest concern is breaking something that currently works. Right now, the parts being changed that could affect other CPU types would be related to a small refactoring of how the features are organized, and that would be seen right away when trying to start a new VM after the package is installed. * Other tests, related to the features being backported, are being done by our KVM regression tests, including migration combinations, to reduce chances that a regression is introduced. [Other Info] * N/A To manage notifications about this bug go to: https://bugs.launchpad.net/intel/+bug/1828495/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
