Re: [PATCH v2 3/3] paravirt: rename paravirt_enabled to paravirt_legacy

[Boris Ostrovsky]

On 02/06/2016 03:59 AM, Luis R. Rodriguez wrote:
> The enumeration of legacy crap by ACPI boot flags seems to provide enough
> details to suit our needs if we really wanted to zero down on the specifics of
> what paravirt_legacy() means, there are these flags:
>
> /* Masks for FADT IA-PC Boot Architecture Flags (boot_flags) [Vx]=Introduced in this FADT revision */
> #define ACPI_FADT_LEGACY_DEVICES    (1)         /* 00: [V2] System has LPC or ISA bus devices */
> #define ACPI_FADT_8042              (1<<1)      /* 01: [V3] System has an 8042 controller on port 60/64 */
> #define ACPI_FADT_NO_VGA            (1<<2)      /* 02: [V4] It is not safe to probe for VGA hardware */
> #define ACPI_FADT_NO_MSI            (1<<3)      /* 03: [V4] Message Signaled Interrupts (MSI) must not be enabled */
> #define ACPI_FADT_NO_ASPM           (1<<4)      /* 04: [V4] PCIe ASPM control must not be enabled */
> #define ACPI_FADT_NO_CMOS_RTC       (1<<5)      /* 05: [V5] No CMOS real-time clock present */
>
> I checked and I didn't see qemu using any of the ACPI boot flags,
> but I suspected qemu instances must use a series of legacy crap.
> Likewise for KVM.
>
> coreboot defines legacy free when you don't have any of the above flags set:
> #define ACPI_FADT_LEGACY_FREE   0x00    /* No legacy devices (including 8042) *
>
> Would it be sufficient to just stick to "pv legacy" equivalent
> of requiring just ACPI_FADT_LEGACY_DEVICES and ACPI_FADT_8042 ?

I believe unprivileged PV guests may be compiled without CONFIG_ACPI if 
you are talking about requiring (or manually setting) these flags.

-boris

> I should point out It turns out ACPI_FADT_NO_CMOS_RTC matches lguest's and it
> seems that's the only reason we have that RTC PV flag and the features pv
> field... with the linker table + x86 subarch use it should be relatively simple
> to remove paravirt_has_feature() paravirt_has() and PV_SUPPORTED_RTC. lguest
> would just be the only subarch that opts out.
>
>    Luis