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    SubjectRe: [RFC PATCH 1/1] platform-msi: Add platform check for subdevice irq domain
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    Hi Bjorn,

    On 12/11/20 2:57 AM, Bjorn Helgaas wrote:
    > On Thu, Dec 10, 2020 at 08:46:24AM +0800, Lu Baolu wrote:
    >> The pci_subdevice_msi_create_irq_domain() should fail if the underlying
    >> platform is not able to support IMS (Interrupt Message Storage). Otherwise,
    >> the isolation of interrupt is not guaranteed.
    >>
    >> For x86, IMS is only supported on bare metal for now. We could enable it
    >> in the virtualization environments in the future if interrupt HYPERCALL
    >> domain is supported or the hardware has the capability of interrupt
    >> isolation for subdevices.
    >
    >> + * We want to figure out which context we are running in. But the hardware
    >> + * does not introduce a reliable way (instruction, CPUID leaf, MSR, whatever)
    >> + * which can be manipulated by the VMM to let the OS figure out where it runs.
    >> + * So we go with the below probably_on_bare_metal() function as a replacement
    >> + * for definitely_on_bare_metal() to go forward only for the very simple reason
    >> + * that this is the only option we have.
    >> + */
    >> +static const char * const possible_vmm_vendor_name[] = {
    >> + "QEMU", "Bochs", "KVM", "Xen", "VMware", "VMW", "VMware Inc.",
    >> + "innotek GmbH", "Oracle Corporation", "Parallels", "BHYVE",
    >> + "Microsoft Corporation"
    >> +};
    >> +
    >> +static bool probably_on_bare_metal(void)
    >
    > What is the point of a function called probably_on_bare_metal()?
    > *Probably*? The caller can't really do anything with the fact that
    > we're not 100% sure this gives the correct answer. Just call it
    > "on_bare_metal()" or something and accept the fact that it might be
    > wrong sometimes.

    Agreed. we can use on_bare_metal() and add comments and kernel messages
    to let users and developers know that we're not 100% sure. People should
    help to make it more accurate by reporting exceptions.

    >
    > This patch goes with IMS support, which somebody else is handling, so
    > I assume you don't need anything from the PCI side.

    Yes. This is a followup of previous discussion.

    Best regards,
    baolu

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