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From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: Sasha Levin <sashal@kernel.org>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	Leonardo Bras <leobras@redhat.com>,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	dave.hansen@linux.intel.com, x86@kernel.org,
	chang.seok.bae@intel.com, luto@kernel.org, kvm@vger.kernel.org,
	Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH AUTOSEL 5.16 07/28] x86/kvm/fpu: Limit guest user_xfeatures to supported bits of XCR0
Date: Tue, 7 Jun 2022 14:54:14 +0200	[thread overview]
Message-ID: <9d336622-6964-454a-605f-1ca90b902836@redhat.com> (raw)
In-Reply-To: <Yp5xSi6P3q187+A+@xz-m1.local>

On 6/6/22 23:27, Peter Xu wrote:
> On Mon, Jun 06, 2022 at 06:18:12PM +0200, Paolo Bonzini wrote:
>>> However there seems to be something missing at least to me, on why it'll
>>> fail a migration from 5.15 (without this patch) to 5.18 (with this patch).
>>> In my test case, user_xfeatures will be 0x7 (FP|SSE|YMM) if without this
>>> patch, but 0x0 if with it.
>>
>> What CPU model are you using for the VM?
> 
> I didn't specify it, assuming it's qemu64 with no extra parameters.

Ok, so indeed it lacks AVX and this patch can have an effect.

>> For example, if the source lacks this patch but the destination has it,
>> the source will transmit YMM registers, but the destination will fail to
>> set them if they are not available for the selected CPU model.
>>
>> See the commit message: "As a bonus, it will also fail if userspace tries to
>> set fpu features (with the KVM_SET_XSAVE ioctl) that are not compatible to
>> the guest configuration.  Such features will never be returned by
>> KVM_GET_XSAVE or KVM_GET_XSAVE2."
> 
> IIUC you meant we should have failed KVM_SET_XSAVE when they're not aligned
> (probably by failing validate_user_xstate_header when checking against the
> user_xfeatures on dest host). But that's probably not my case, because here
> KVM_SET_XSAVE succeeded, it's just that the guest gets a double fault after
> the precopy migration completes (or for postcopy when the switchover is
> done).

Difficult to say what's happening without seeing at least the guest code 
around the double fault (above you said "fail a migration" and I thought 
that was a different scenario than the double fault), and possibly which 
was the first exception that contributed to the double fault.

Paolo


  reply	other threads:[~2022-06-07 12:55 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-01 20:13 [PATCH AUTOSEL 5.16 01/28] selftests/bpf: Add test for bpf_timer overwriting crash Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 02/28] swiotlb: fix info leak with DMA_FROM_DEVICE Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 03/28] usb: dwc3: pci: add support for the Intel Raptor Lake-S Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 04/28] pinctrl: tigerlake: Revert "Add Alder Lake-M ACPI ID" Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 05/28] KVM: Fix lockdep false negative during host resume Sasha Levin
2022-03-01 20:19   ` Paolo Bonzini
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 06/28] kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode Sasha Levin
2022-03-01 20:19   ` Paolo Bonzini
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 07/28] x86/kvm/fpu: Limit guest user_xfeatures to supported bits of XCR0 Sasha Levin
2022-03-01 20:22   ` Paolo Bonzini
2022-06-03 18:40     ` Peter Xu
2022-06-06 16:18       ` Paolo Bonzini
2022-06-06 21:27         ` Peter Xu
2022-06-07 12:54           ` Paolo Bonzini [this message]
2022-06-07 15:04             ` Sean Christopherson
2022-06-07 18:17               ` Peter Xu
2022-06-07 18:47                 ` Sean Christopherson
2022-06-07 21:01                   ` Peter Xu
2022-06-07 18:55                 ` Peter Xu
2022-06-08 20:34                   ` Leonardo Bras Soares Passos
2022-06-08 20:53                     ` Peter Xu
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 08/28] spi: rockchip: Fix error in getting num-cs property Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 09/28] spi: rockchip: terminate dma transmission when slave abort Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 10/28] drm/vc4: hdmi: Unregister codec device on unbind Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 11/28] of/fdt: move elfcorehdr reservation early for crash dump kernel Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 12/28] x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU Sasha Levin
2022-03-01 20:17   ` Paolo Bonzini
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 13/28] drivers: hamradio: 6pack: fix UAF bug caused by mod_timer() Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 14/28] net-sysfs: add check for netdevice being present to speed_show Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 15/28] sr9700: sanity check for packet length Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 16/28] hwmon: (pmbus) Clear pmbus fault/warning bits after read Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 17/28] nvme-tcp: send H2CData PDUs based on MAXH2CDATA Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 18/28] PCI: Mark all AMD Navi10 and Navi14 GPU ATS as broken Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 19/28] gpio: Return EPROBE_DEFER if gc->to_irq is NULL Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 20/28] drm/amdgpu: bypass tiling flag check in virtual display case (v2) Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 21/28] Revert "xen-netback: remove 'hotplug-status' once it has served its purpose" Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 22/28] Revert "xen-netback: Check for hotplug-status existence before watching" Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 23/28] ipv6: prevent a possible race condition with lifetimes Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 24/28] tracing: Ensure trace buffer is at least 4096 bytes large Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 25/28] tracing/osnoise: Make osnoise_main to sleep for microseconds Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 26/28] tracing: Fix selftest config check for function graph start up test Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 27/28] selftest/vm: fix map_fixed_noreplace test failure Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 28/28] selftests/memfd: clean up mapping in mfd_fail_write Sasha Levin

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