KVM: SVM: make svm_flush_tlb_gva do a full asid flush if NPT enabled

Red Hat is seeing multiple reports of Windows memory corruptions
(and consequent BSODs) with hv-tlbflush=on, on AMD processors only.
The crashes, while extremely rare, happen even with a stock configuration,
but with Driver Verifier enabled they can be detected after approximately
200 VM hours.  In particular, Alexander Lougovski measured the following:

- on AMD Turin, 15 crashes in 3300 VM hours

- on AMD Milan, 2 crashes in 500 VM hours (there are fewer hours
  here due to the host being smaller)

- on Intel Sapphire Rapids, 0 crashes in 8000 VM hours

- on AMD Turin with full TLB flush (not exactly this patch but
  similar), no crashes in ~2 weeks of run time which should also
  be ~7000 VM hours

For Turin, the microcode version was 0x0b002162, which (assuming
this is the same issue) should not be affected by the problem listed in
https://knowledge.broadcom.com/external/article/419026/bsod-on-virtual-machines-running-on-amd.html;
on the other hand that problem should not apply to earlier processors.
AMD has not provided any information or analysis yet, and when we asked
we didn't know yet that it reproduced on Milan as well.

As to the workload, Alexander threw more or less everything at the same
time at the VM:

- a full Windows Defender scan every 30 minutes

- a disk I/O job

- a loop doing repeated mmap of system files (mostly to hope that
  it triggers some consistency check in the Windows memory manager)

- SQL Express 2022 + StressDB (1.6M rows), with the host doing queries
  (75% write/25% read) via sqlcmd

Driver Verifier is able to detect BSODs more or less at the same time as
the pages are freed.  They mostly happen in the Windows Defender filter
driver, but occasionally also in the networking stack (e.g., afd.sys)
or elsewhere in the filesystem stack (e.g., fltmgr.sys).

The flush is issued from kvm_hv_vcpu_flush_tlb(), which receives the
cross-CPU requests from the Hyper-V TLB flush hypercalls via a kfifo
and is invoked by the KVM_REQ_HV_TLB_FLUSH request.  The mechanism is
the same for both Intel and AMD, and the handler for both vendors is
a simple INVVPID(ADDR)/INVLPGA instruction.

Because the request is handled on the destination CPU, there is a question
of what happens if the VM is migrated across physical CPUs.  In that case,
the INVLPGA instruction would use a stale svm->vmcb->control.asid; but
if anything that might do an *unnecessary* flush (on an asid that's being
used for another VM) and then pre_svm_run() would force a full TLB rebuild.

So, for lack of better ideas, this patch forces a full ASID bump in
svm_flush_tlb_gva().  To avoid paying the price on Intel and also to
avoid unnecessary loops on AMD, the flush_tlb_gva op now returns whether
it did a full flush or not; kvm_hv_vcpu_flush_tlb() takes note and exits
its loops immediately.  While there is an obvious performance impact,
about half of the benefit from Hyper-V tlbflush is preserved (10% vs. 20%
on the SQL Server workload).

kvm_mmu_invalidate_addr() is the only other caller of the flush_tlb_gva op.
The change would have a performance impact on every intercepted INVLPG and,
for nested SVM, on every L1 INVLPGA.  For INVLPGA specifically, this covers
the same suspected issue but for nested hypervisors, so it is correct to
apply the workaround; for INVLPG on shadow paging, instead, the impact
would be stronger and, due to lack of data, for now the use of INVLPGA is
left in place in svm_flush_tlb_gva().

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

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