linux-kernel - [REGRESSION] Commit 5745392e0c2b ("PCI: Apply the new generic I/O management on PCI IO hosts") breaks PCI for legacy virtio devices with kvmtool on arm64

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Message-ID: <20180907174140.GI12788@arm.com>
Date:   Fri, 7 Sep 2018 18:41:40 +0100
From:   Will Deacon <will.deacon@....com>
To:     yuanzhichang@...ilicon.com, dann.frazier@...onical.com,
        gabriele.paoloni@...wei.com, arnd@...db.de, bhelgaas@...gle.com,
        andy.shevchenko@...il.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, suzuki.poulose@....com,
        jean-philippe.brucker@....com
Subject: [REGRESSION] Commit 5745392e0c2b ("PCI: Apply the new generic I/O
 management on PCI IO hosts") breaks PCI for legacy virtio devices with
 kvmtool on arm64

Hi all,

I'm seeing a regression in Linux guests since 4.17 under kvmtool, where
legacy virtio devices using the PCI transport fail to probe. Legacy virtio
PCI devices must be accessed via "I/O space" (e.g. BAR0, which is
IORESOURCE_IO) and kvmtool assigns this to the guest physical range
0x0 - 0x10000.

On arm64, when the virtio legacy PCI driver calls pci_iomap() for this BAR,
it expands to ioport_map():

  static inline void __iomem *ioport_map(unsigned long port, unsigned int nr)
  {
  	return PCI_IOBASE + (port & MMIO_UPPER_LIMIT);
  }

Since the indirect PIO changes, MMIO_UPPER_LIMIT is defined as:

  /*
   * We reserve 0x4000 bytes for Indirect IO as so far this library is only
   * used by the HiSilicon LPC Host. If needed, we can reserve a wider IO
   * area by redefining the macro below.
   */
  #define PIO_INDIRECT_SIZE 0x4000
  #define MMIO_UPPER_LIMIT (IO_SPACE_LIMIT - PIO_INDIRECT_SIZE)

which corrupts the BAR address. For example, kvmtool has the BAR pointing
at 0x6200 on my system, but pci_iomap() actually maps offset 0x2200.
Changing PIO_INDIRECT_SIZE to 0 gets things working again.

Since this stuff doesn't revert nicely, I'm not sure how to proceed. Any
thoughts? Generally, having a per-platform magic constant hardcoded in
the PCI mapping code makes me feel slightly ill...

Cheers,

Will