Commit dd6d87 breaks serial console

Commit dd6d87 breaks serial console

[Roger Pau Monné]

[-- Attachment #1: Type: text/plain, Size: 8606 bytes --]

Hello,

The following commit:

commit dd6d87a4fcc8350c752e389abb3bcd8479c37555
Author: Jan Beulich <jbeulich@suse.com>
Date:   Fri Jun 20 10:26:37 2014 +0200

    VT-d: drop redundant calls to invalidate_sync()

    The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
    invokes invalidate_sync(). Removing the superfluous instances at once
    allows the function to become static.

    Signed-off-by: Jan Beulich <jbeulich@suse.com>
    Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
    Acked-by: Yang Zhang <yang.z.zhang@intel.com>

Breaks serial console on my box, this is all the output I get with this 
commit applied:

PXELINUX 4.02 debian-20101014  Copyright (C) 1994-2010 H. Peter Anvin et al
boot:
Loading xen/xen_pvh7.gz... ok
Loading linux/vmlinuz-3.15.0-rc3+... ok
Loading linux/initrd.img-3.15.0-rc3+... ok
 __  __            _  _    ____                     _        _     _
 \ \/ /___ _ __   | || |  | ___|    _   _ _ __  ___| |_ __ _| |__ | | ___
  \  // _ \ '_ \  | || |_ |___ \ __| | | | '_ \/ __| __/ _` | '_ \| |/ _ \
  /  \  __/ | | | |__   _| ___) |__| |_| | | | \__ \ || (_| | |_) | |  __/
 /_/\_\___|_| |_|    |_|(_)____/    \__,_|_| |_|___/\__\__,_|_.__/|_|\___|

(XEN) Xen version 4.5-unstable (root@) (gcc (FreeBSD Ports Collection) 4.6.4) debug=y Mon Jul 14 18:01:10 CEST 2014
(XEN) Latest ChangeSet: Fri Jul 11 11:32:33 2014 +0800 git:7bddc6b
(XEN) Bootloader: PXELINUX 4.02 debian-20101014
(XEN) Command line: ioapic_ack=old dom0_max_vcpus=6 dom0_mem=1024M com1=115200,8n1 guest_loglvl=all loglvl=all console=com1
(XEN) Video information:
(XEN)  VGA is text mode 80x25, font 8x16
(XEN)  VBE/DDC methods: V2; EDID transfer time: 1 seconds
(XEN) Disc information:
(XEN)  Found 2 MBR signatures
(XEN)  Found 2 EDD information structures
(XEN) Xen-e820 RAM map:
(XEN)  0000000000000000 - 0000000000092400 (usable)
(XEN)  00000000000f0000 - 0000000000100000 (reserved)
(XEN)  0000000000100000 - 00000000dfdf9c00 (usable)
(XEN)  00000000dfdf9c00 - 00000000dfe4bc00 (ACPI NVS)
(XEN)  00000000dfe4bc00 - 00000000dfe4dc00 (ACPI data)
(XEN)  00000000dfe4dc00 - 00000000e0000000 (reserved)
(XEN)  00000000f8000000 - 00000000fd000000 (reserved)
(XEN)  00000000fe000000 - 00000000fed00400 (reserved)
(XEN)  00000000fee00000 - 00000000fef00000 (reserved)
(XEN)  00000000ffb00000 - 0000000100000000 (reserved)
(XEN)  0000000100000000 - 00000001a0000000 (usable)
(XEN) ACPI: RSDP 000FEC30, 0024 (r2 DELL  )
(XEN) ACPI: XSDT 000FCCC7, 007C (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: FACP 000FCDB7, 00F4 (r3 DELL    B10K          15 ASL        61)
(XEN) ACPI: DSDT FFE9E951, 4A74 (r1   DELL    dt_ex     1000 INTL 20050624)
(XEN) ACPI: FACS DFDF9C00, 0040
(XEN) ACPI: SSDT FFEA34D6, 009C (r1   DELL    st_ex     1000 INTL 20050624)
(XEN) ACPI: APIC 000FCEAB, 015E (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: BOOT 000FD009, 0028 (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: ASF! 000FD031, 0096 (r32 DELL    B10K          15 ASL        61)
(XEN) ACPI: MCFG 000FD0C7, 003C (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: HPET 000FD103, 0038 (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: TCPA 000FD35F, 0032 (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: DMAR 000FD391, 00C8 (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: SLIC 000FD13B, 0176 (r1 DELL    B10K          15 ASL        61)
(XEN) ACPI: SSDT DFE4DC00, 276C (r1  INTEL PPM RCM  80000001 INTL 20061109)
(XEN) System RAM: 6141MB (6288940kB)
(XEN) No NUMA configuration found
(XEN) Faking a node at 0000000000000000-00000001a0000000
(XEN) Domain heap initialised
(XEN) DMI 2.5 present.
(XEN) Using APIC driver default
(XEN) ACPI: PM-Timer IO Port: 0x808
(XEN) ACPI: SLEEP INFO: pm1x_cnt[1:804,1:0], pm1x_evt[1:800,1:0]
(XEN) ACPI:             wakeup_vec[dfdf9c0c], vec_size[20]
(XEN) ACPI: Local APIC address 0xfee00000
(XEN) ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled)
(XEN) Processor #0 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x02] lapic_id[0x02] enabled)
(XEN) Processor #2 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x03] lapic_id[0x04] enabled)
(XEN) Processor #4 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x04] lapic_id[0x06] enabled)
(XEN) Processor #6 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x05] lapic_id[0x01] enabled)
(XEN) Processor #1 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x06] lapic_id[0x03] enabled)
(XEN) Processor #3 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x07] lapic_id[0x05] enabled)
(XEN) Processor #5 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x08] lapic_id[0x07] enabled)
(XEN) Processor #7 7:10 APIC version 21
(XEN) ACPI: LAPIC (acpi_id[0x09] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x0a] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x0b] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x0c] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x0d] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x0e] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x0f] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x10] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x11] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x12] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x13] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x14] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x15] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x16] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x17] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x18] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x19] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x1a] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x1b] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x1c] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x1d] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x1e] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x1f] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC (acpi_id[0x20] lapic_id[0x00] disabled)
(XEN) ACPI: LAPIC_NMI (acpi_id[0xff] high level lint[0x1])
(XEN) ACPI: IOAPIC (id[0x08] address[0xfec00000] gsi_base[0])
(XEN) IOAPIC[0]: apic_id 8, version 32, address 0xfec00000, GSI 0-23
(XEN) ACPI: IOAPIC (id[0x09] address[0xfec80000] gsi_base[24])
(XEN) IOAPIC[1]: apic_id 9, version 32, address 0xfec80000, GSI 24-47
(XEN) ACPI: INT_SRC_OVR (bus 0 bus_irq 0 global_irq 2 dfl dfl)
(XEN) ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 high level)
(XEN) ACPI: IRQ0 used by override.
(XEN) ACPI: IRQ2 used by override.
(XEN) ACPI: IRQ9 used by override.
(XEN) Enabling APIC mode:  Flat.  Using 2 I/O APICs
(XEN) ACPI: HPET id: 0x8086a301 base: 0xfed00000
(XEN) ERST table was not found
(XEN) Using ACPI (MADT) for SMP configuration information
(XEN) SMP: Allowing 32 CPUs (24 hotplug CPUs)
(XEN) IRQ limits: 48 GSI, 1504 MSI/MSI-X
(XEN) Using scheduler: SMP Credit Scheduler (credit)
(XEN) Detected 3066.835 MHz processor.
(XEN) Initing memory sharing.
(XEN) mce_intel.c:719: MCA Capability: BCAST 1 SER 0 CMCI 1 firstbank 0 extended MCE MSR 0
(XEN) Intel machine check reporting enabled
(XEN) alt table ffff82d0802d0450 -> ffff82d0802d1050
(XEN) PCI: MCFG configuration 0: base f8000000 segment 0000 buses 00 - 3f
(XEN) PCI: MCFG area at f8000000 reserved in E820
(XEN) PCI: Using MCFG for segment 0000 bus 00-3f
(XEN) Intel VT-d iommu 0 supported page sizes: 4kB.
(XEN) Intel VT-d Snoop Control enabled.
(XEN) Intel VT-d Dom0 DMA Passthrough not enabled.
(XEN) Intel VT-d Queued Invalidation enabled.
(XEN) Intel VT-d Interrupt Remapping enabled.
(XEN) Intel VT-d Shared EPT tables not enabled.
(XEN) I/O virtualisation enabled
(XEN)  - Dom0 mode: Relaxed
(XEN) Interrupt remapping enabled
(XEN) ENABLING IO-APIC IRQs
(XEN)  -> Using old ACK method
(XEN) ..TIMER: vector=0xF0 apic1=0 pin1=2 apic2=-1 pin2=-1
(XEN) Platform timer is 14.318MHz HPET
(XEN) Allocated console ring of 64 KiB.
(XEN) mwait-idle: MWAIT substates: 0x1120
(XEN) mwait-idle: v0.4 model 0x1a
(XEN) mwait-idle: lapic_timer_reliable_states 0x2
(XEN) HPET: 0 timers usable for broadcast (4 total)
(XEN) VMX: Supported advanced features:
(XEN)  - APIC MMIO access virtualisation
(XEN)  - APIC TPR shadow
(XEN)  - Extended Page Tables (EPT)
(XEN)  - Virtual-Processor Identifiers (VPID)
(XEN)  - Virtual NMI
(XEN)  - MSR direct-access bitmap
(XEN) HVM: ASIDs enabled.
(XEN) HVM: VMX enabled
(XEN) HVM: Hardware Assisted Paging (HAP) detected
(XEN) HVM: HAP page sizes: 4kB, 2MB
(

I'm attaching a revert of this patch, which makes serial output on my 
box work as expected.

Roger.

[-- Attachment #2: 0001-Revert-VT-d-drop-redundant-calls-to-invalidate_sync.patch --]
[-- Type: text/plain, Size: 2877 bytes --]

>From 0d3f767f4cd5a30909b8c9d76e15e10a45d7a05d Mon Sep 17 00:00:00 2001
From: Roger Pau Monne <roger.pau@citrix.com>
Date: Mon, 14 Jul 2014 17:54:49 +0200
Subject: [PATCH] Revert "VT-d: drop redundant calls to invalidate_sync()"

This reverts commit dd6d87a4fcc8350c752e389abb3bcd8479c37555.

The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
invokes invalidate_sync(). Removing the superfluous instances at once
allows the function to become static.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Yang Zhang <yang.z.zhang@intel.com>
---
 xen/drivers/passthrough/vtd/extern.h   |    1 +
 xen/drivers/passthrough/vtd/intremap.c |    2 ++
 xen/drivers/passthrough/vtd/qinval.c   |    2 +-
 3 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/extern.h b/xen/drivers/passthrough/vtd/extern.h
index 5524dba..92ec343 100644
--- a/xen/drivers/passthrough/vtd/extern.h
+++ b/xen/drivers/passthrough/vtd/extern.h
@@ -42,6 +42,7 @@ void iommu_flush_cache_page(void *addr, unsigned long npages);
 int iommu_alloc(struct acpi_drhd_unit *drhd);
 void iommu_free(struct acpi_drhd_unit *drhd);
 
+int invalidate_sync(struct iommu *iommu);
 int iommu_flush_iec_global(struct iommu *iommu);
 int iommu_flush_iec_index(struct iommu *iommu, u8 im, u16 iidx);
 void clear_fault_bits(struct iommu *iommu);
diff --git a/xen/drivers/passthrough/vtd/intremap.c b/xen/drivers/passthrough/vtd/intremap.c
index 0333686..07c6dac 100644
--- a/xen/drivers/passthrough/vtd/intremap.c
+++ b/xen/drivers/passthrough/vtd/intremap.c
@@ -358,6 +358,7 @@ static int ioapic_rte_to_remap_entry(struct iommu *iommu,
     memcpy(iremap_entry, &new_ire, sizeof(struct iremap_entry));
     iommu_flush_cache_entry(iremap_entry, sizeof(struct iremap_entry));
     iommu_flush_iec_index(iommu, 0, index);
+    invalidate_sync(iommu);
 
     unmap_vtd_domain_page(iremap_entries);
     spin_unlock_irqrestore(&ir_ctrl->iremap_lock, flags);
@@ -642,6 +643,7 @@ static int msi_msg_to_remap_entry(
     memcpy(iremap_entry, &new_ire, sizeof(struct iremap_entry));
     iommu_flush_cache_entry(iremap_entry, sizeof(struct iremap_entry));
     iommu_flush_iec_index(iommu, 0, index);
+    invalidate_sync(iommu);
 
     unmap_vtd_domain_page(iremap_entries);
     spin_unlock_irqrestore(&ir_ctrl->iremap_lock, flags);
diff --git a/xen/drivers/passthrough/vtd/qinval.c b/xen/drivers/passthrough/vtd/qinval.c
index 4603020..deee376 100644
--- a/xen/drivers/passthrough/vtd/qinval.c
+++ b/xen/drivers/passthrough/vtd/qinval.c
@@ -181,7 +181,7 @@ static int queue_invalidate_wait(struct iommu *iommu,
     return -EOPNOTSUPP;
 }
 
-static int invalidate_sync(struct iommu *iommu)
+int invalidate_sync(struct iommu *iommu)
 {
     struct qi_ctrl *qi_ctrl = iommu_qi_ctrl(iommu);
 
-- 
1.7.7.5 (Apple Git-26)


[-- Attachment #3: Type: text/plain, Size: 126 bytes --]

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Re: Commit dd6d87 breaks serial console

[Andrew Cooper]

On 14/07/14 17:07, Roger Pau Monné wrote:
> Hello,
>
> The following commit:
>
> commit dd6d87a4fcc8350c752e389abb3bcd8479c37555
> Author: Jan Beulich <jbeulich@suse.com>
> Date:   Fri Jun 20 10:26:37 2014 +0200
>
>     VT-d: drop redundant calls to invalidate_sync()
>
>     The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
>     invokes invalidate_sync(). Removing the superfluous instances at once
>     allows the function to become static.
>
>     Signed-off-by: Jan Beulich <jbeulich@suse.com>
>     Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>     Acked-by: Yang Zhang <yang.z.zhang@intel.com>
>
> Breaks serial console on my box, this is all the output I get with this 
> commit applied:

Are you sure you have bisected this correctly?

Unless there is some hardware side-effect of issuing two qinvalidate
wait descriptors back-to-back, the change still looks to be good. 
Alternately, are we missing a hardware erratum for your system?

~Andrew

Re: Commit dd6d87 breaks serial console

[Roger Pau Monné]

On 14/07/14 18:25, Andrew Cooper wrote:
> On 14/07/14 17:07, Roger Pau Monné wrote:
>> Hello,
>>
>> The following commit:
>>
>> commit dd6d87a4fcc8350c752e389abb3bcd8479c37555
>> Author: Jan Beulich <jbeulich@suse.com>
>> Date:   Fri Jun 20 10:26:37 2014 +0200
>>
>>     VT-d: drop redundant calls to invalidate_sync()
>>
>>     The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
>>     invokes invalidate_sync(). Removing the superfluous instances at once
>>     allows the function to become static.
>>
>>     Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>     Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>     Acked-by: Yang Zhang <yang.z.zhang@intel.com>
>>
>> Breaks serial console on my box, this is all the output I get with this 
>> commit applied:
> 
> Are you sure you have bisected this correctly?
> 
> Unless there is some hardware side-effect of issuing two qinvalidate
> wait descriptors back-to-back, the change still looks to be good. 
> Alternately, are we missing a hardware erratum for your system?

Just for the record, setting iommu=no-intremap solves the problem, so
I'm quite sure I've bisected it right. This is on a Xeon W3550, I can
provide whatever other hardware information is needed.

Roger.

Re: Commit dd6d87 breaks serial console

[Zhang, Yang Z]

Roger Pau Monné wrote on 2014-07-15:
> On 14/07/14 18:25, Andrew Cooper wrote:
>> On 14/07/14 17:07, Roger Pau Monné wrote:
>>> Hello,
>>> 
>>> The following commit:
>>> 
>>> commit dd6d87a4fcc8350c752e389abb3bcd8479c37555
>>> Author: Jan Beulich <jbeulich@suse.com>
>>> Date:   Fri Jun 20 10:26:37 2014 +0200
>>> 
>>>     VT-d: drop redundant calls to invalidate_sync()
>>>     
>>>     The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
>>>     invokes invalidate_sync(). Removing the superfluous instances at once
>>>     allows the function to become static.
>>>     
>>>     Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>>     Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>>     Acked-by: Yang Zhang <yang.z.zhang@intel.com>
>>> Breaks serial console on my box, this is all the output I get with
>>> this commit applied:
>> 
>> Are you sure you have bisected this correctly?
>> 
>> Unless there is some hardware side-effect of issuing two qinvalidate
>> wait descriptors back-to-back, the change still looks to be good.
>> Alternately, are we missing a hardware erratum for your system?
> 
> Just for the record, setting iommu=no-intremap solves the problem, so
> I'm quite sure I've bisected it right. This is on a Xeon W3550, I can
> provide whatever other hardware information is needed.

It is so strange. The patch is really simple. Does Xen still alive when serial console breaks? Also, can you try to add invalidate_sync one by one to figure which one caused the problem?

> 
> Roger.


Best regards,
Yang

Re: Commit dd6d87 breaks serial console

[Roger Pau Monné]

On 15/07/14 03:24, Zhang, Yang Z wrote:
> Roger Pau Monné wrote on 2014-07-15:
>> On 14/07/14 18:25, Andrew Cooper wrote:
>>> On 14/07/14 17:07, Roger Pau Monné wrote:
>>>> Hello,
>>>>
>>>> The following commit:
>>>>
>>>> commit dd6d87a4fcc8350c752e389abb3bcd8479c37555
>>>> Author: Jan Beulich <jbeulich@suse.com>
>>>> Date:   Fri Jun 20 10:26:37 2014 +0200
>>>>
>>>>     VT-d: drop redundant calls to invalidate_sync()
>>>>     
>>>>     The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
>>>>     invokes invalidate_sync(). Removing the superfluous instances at once
>>>>     allows the function to become static.
>>>>     
>>>>     Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>>>     Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>>>     Acked-by: Yang Zhang <yang.z.zhang@intel.com>
>>>> Breaks serial console on my box, this is all the output I get with
>>>> this commit applied:
>>>
>>> Are you sure you have bisected this correctly?
>>>
>>> Unless there is some hardware side-effect of issuing two qinvalidate
>>> wait descriptors back-to-back, the change still looks to be good.
>>> Alternately, are we missing a hardware erratum for your system?
>>
>> Just for the record, setting iommu=no-intremap solves the problem, so
>> I'm quite sure I've bisected it right. This is on a Xeon W3550, I can
>> provide whatever other hardware information is needed.
> 
> It is so strange. The patch is really simple. Does Xen still alive when serial console breaks? Also, can you try to add invalidate_sync one by one to figure which one caused the problem?

Yes, Xen seems to work fine (apart from the serial console), I can
access Dom0 using ssh and create guests.

The invalidate_sync that prevents this problem is the one in
ioapic_rte_to_remap_entry, I have successfully removed the other
invalidate_sync in msi_msg_to_remap_entry without problems.

Roger.

Re: Commit dd6d87 breaks serial console

[Jan Beulich]

>>> On 23.07.14 at 10:31, <roger.pau@citrix.com> wrote:
> On 15/07/14 03:24, Zhang, Yang Z wrote:
>> It is so strange. The patch is really simple. Does Xen still alive when 
> serial console breaks? Also, can you try to add invalidate_sync one by one to 
> figure which one caused the problem?
> 
> Yes, Xen seems to work fine (apart from the serial console), I can
> access Dom0 using ssh and create guests.
> 
> The invalidate_sync that prevents this problem is the one in
> ioapic_rte_to_remap_entry, I have successfully removed the other
> invalidate_sync in msi_msg_to_remap_entry without problems.

That's meaningless, as MSI isn't involved in serial console handling.

Jan

Re: Commit dd6d87 breaks serial console

[Jan Beulich]

>>> On 14.07.14 at 18:07, <roger.pau@citrix.com> wrote:
> The following commit:
> 
> commit dd6d87a4fcc8350c752e389abb3bcd8479c37555
> Author: Jan Beulich <jbeulich@suse.com>
> Date:   Fri Jun 20 10:26:37 2014 +0200
> 
>     VT-d: drop redundant calls to invalidate_sync()
> 
>     The call tree iommu_flush_iec_index() -> __iommu_flush_iec() already
>     invokes invalidate_sync(). Removing the superfluous instances at once
>     allows the function to become static.
> 
>     Signed-off-by: Jan Beulich <jbeulich@suse.com>
>     Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>     Acked-by: Yang Zhang <yang.z.zhang@intel.com>
> 
> Breaks serial console on my box, this is all the output I get with this 
> commit applied:
> [...]
> I'm attaching a revert of this patch, which makes serial output on my 
> box work as expected.

Just to augment what others already said - in situations like this,
requesting a revert without any understanding/explanation of
what's actually wrong, or at least under what specific conditions
the issue occurs (since clearly the serial console has been working
fine for me and likely others) is generally insufficient.

Jan