Commit da66761c authored Mar 20, 2019 by Vitaly Kuznetsov Committed by Paolo Bonzini Apr 18, 2019

x86: kvm: hyper-v: deal with buggy TLB flush requests from WS2012



It was reported that with some special Multi Processor Group configuration,
e.g:
 bcdedit.exe /set groupsize 1
 bcdedit.exe /set maxgroup on
 bcdedit.exe /set groupaware on
for a 16-vCPU guest WS2012 shows BSOD on boot when PV TLB flush mechanism
is in use.

Tracing kvm_hv_flush_tlb immediately reveals the issue:

 kvm_hv_flush_tlb: processor_mask 0x0 address_space 0x0 flags 0x2

The only flag set in this request is HV_FLUSH_ALL_VIRTUAL_ADDRESS_SPACES,
however, processor_mask is 0x0 and no HV_FLUSH_ALL_PROCESSORS is specified.
We don't flush anything and apparently it's not what Windows expects.

TLFS doesn't say anything about such requests and newer Windows versions
seem to be unaffected. This all feels like a WS2012 bug, which is, however,
easy to workaround in KVM: let's flush everything when we see an empty
flush request, over-flushing doesn't hurt.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent c09d65d9

arch/x86/kvm/hyperv.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -1371,7 +1371,16 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *current_vcpu, u64 ingpa,

		valid_bank_mask = BIT_ULL(0);
		sparse_banks[0] = flush.processor_mask;
		all_cpus = flush.flags & HV_FLUSH_ALL_PROCESSORS;

		/*
		* Work around possible WS2012 bug: it sends hypercalls
		* with processor_mask = 0x0 and HV_FLUSH_ALL_PROCESSORS clear,
		* while also expecting us to flush something and crashing if
		* we don't. Let's treat processor_mask == 0 same as
		* HV_FLUSH_ALL_PROCESSORS.
		*/
		all_cpus = (flush.flags & HV_FLUSH_ALL_PROCESSORS) \|\|
		flush.processor_mask == 0;
		} else {
		if (unlikely(kvm_read_guest(kvm, ingpa, &flush_ex,
		sizeof(flush_ex))))

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