Re: [Xen-devel] [PATCH for-4.9] docs: remove PVHv1 document

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

(Using the correct address for Julien)

On Mon, May 29, 2017 at 06:29:48PM +0100, Roger Pau Monne wrote:
> The current misc/pvh.markdown document refers to PVHv1, remove it to
> avoid confusion with PVHv2 since the PVHv1 code has already been
> removed.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Tim Deegan <tim@xxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  docs/misc/pvh.markdown | 377 
> -------------------------------------------------
>  1 file changed, 377 deletions(-)
>  delete mode 100644 docs/misc/pvh.markdown
> 
> diff --git a/docs/misc/pvh.markdown b/docs/misc/pvh.markdown
> deleted file mode 100644
> index 52d8e743e7..0000000000
> --- a/docs/misc/pvh.markdown
> +++ /dev/null
> @@ -1,377 +0,0 @@
> -# PVH Specification #
> -
> -## Rationale ##
> -
> -PVH is a new kind of guest that has been introduced on Xen 4.4 as a DomU, and
> -on Xen 4.5 as a Dom0. The aim of PVH is to make use of the hardware
> -virtualization extensions present in modern x86 CPUs in order to
> -improve performance.
> -
> -PVH is considered a mix between PV and HVM, and can be seen as a PV guest
> -that runs inside of an HVM container, or as a PVHVM guest without any 
> emulated
> -devices. The design goal of PVH is to provide the best performance possible 
> and
> -to reduce the amount of modifications needed for a guest OS to run in this 
> mode
> -(compared to pure PV).
> -
> -This document tries to describe the interfaces used by PVH guests, focusing
> -on how an OS should make use of them in order to support PVH.
> -
> -## Early boot ##
> -
> -PVH guests use the PV boot mechanism, that means that the kernel is loaded 
> and
> -directly launched by Xen (by jumping into the entry point). In order to do 
> this
> -Xen ELF Notes need to be added to the guest kernel, so that they contain the
> -information needed by Xen. Here is an example of the ELF Notes added to the
> -FreeBSD amd64 kernel in order to boot as PVH:
> -
> -    ELFNOTE(Xen, XEN_ELFNOTE_GUEST_OS,       .asciz, "FreeBSD")
> -    ELFNOTE(Xen, XEN_ELFNOTE_GUEST_VERSION,  .asciz, 
> __XSTRING(__FreeBSD_version))
> -    ELFNOTE(Xen, XEN_ELFNOTE_XEN_VERSION,    .asciz, "xen-3.0")
> -    ELFNOTE(Xen, XEN_ELFNOTE_VIRT_BASE,      .quad,  KERNBASE)
> -    ELFNOTE(Xen, XEN_ELFNOTE_PADDR_OFFSET,   .quad,  KERNBASE)
> -    ELFNOTE(Xen, XEN_ELFNOTE_ENTRY,          .quad,  xen_start)
> -    ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, .quad,  hypercall_page)
> -    ELFNOTE(Xen, XEN_ELFNOTE_HV_START_LOW,   .quad,  HYPERVISOR_VIRT_START)
> -    ELFNOTE(Xen, XEN_ELFNOTE_FEATURES,       .asciz, 
> "writable_descriptor_tables|auto_translated_physmap|supervisor_mode_kernel|hvm_callback_vector")
> -    ELFNOTE(Xen, XEN_ELFNOTE_PAE_MODE,       .asciz, "yes")
> -    ELFNOTE(Xen, XEN_ELFNOTE_L1_MFN_VALID,   .long,  PG_V, PG_V)
> -    ELFNOTE(Xen, XEN_ELFNOTE_LOADER,         .asciz, "generic")
> -    ELFNOTE(Xen, XEN_ELFNOTE_SUSPEND_CANCEL, .long,  0)
> -    ELFNOTE(Xen, XEN_ELFNOTE_BSD_SYMTAB,     .asciz, "yes")
> -
> -On the Linux side, the above can be found in `arch/x86/xen/xen-head.S`.
> -
> -It is important to highlight the following notes:
> -
> -  * `XEN_ELFNOTE_ENTRY`: contains the virtual memory address of the kernel 
> entry
> -    point.
> -  * `XEN_ELFNOTE_HYPERCALL_PAGE`: contains the virtual memory address of the
> -    hypercal page inside of the guest kernel (this memory region will be 
> filled
> -    by Xen prior to booting).
> -  * `XEN_ELFNOTE_FEATURES`: contains the list of features supported by the 
> kernel.
> -    In the example above the kernel is only able to boot as a PVH guest, but
> -    those options can be mixed with the ones used by pure PV guests in order 
> to
> -    have a kernel that supports both PV and PVH (like Linux). The list of
> -    options available can be found in the `features.h` public header. Note 
> that
> -    in the example above `hvm_callback_vector` is in `XEN_ELFNOTE_FEATURES`.
> -    Older hypervisors will balk at this being part of it, so it can also be 
> put
> -    in `XEN_ELFNOTE_SUPPORTED_FEATURES` which older hypervisors will ignore.
> -
> -Xen will jump into the kernel entry point defined in `XEN_ELFNOTE_ENTRY` with
> -paging enabled (either long mode or protected mode with paging turned on
> -depending on the kernel bitness) and some basic page tables setup. An 
> important
> -distinction for a 64bit PVH is that it is launched at privilege level 0 as
> -opposed to a 64bit PV guest which is launched at privilege level 3.
> -
> -Also, the `rsi` (`esi` on 32bits) register is going to contain the virtual
> -memory address where Xen has placed the `start_info` structure. The `rsp` 
> (`esp`
> -on 32bits) will point to the top of an initial single page stack, that can be
> -used by the guest kernel. The `start_info` structure contains all the info 
> the
> -guest needs in order to initialize. More information about the contents can 
> be
> -found in the `xen.h` public header.
> -
> -### Initial amd64 control registers values ###
> -
> -Initial values for the control registers are set up by Xen before booting the
> -guest kernel. The guest kernel can expect to find the following features
> -enabled by Xen.
> -
> -`CR0` has the following bits set by Xen:
> -
> -  * PE (bit 0): protected mode enable.
> -  * ET (bit 4): 387 or newer processor.
> -  * PG (bit 31): paging enabled.
> -
> -`CR4` has the following bits set by Xen:
> -
> -  * PAE (bit 5): PAE enabled.
> -
> -And finally in `EFER` the following features are enabled:
> -
> -  * LME (bit 8): Long mode enable.
> -  * LMA (bit 10): Long mode active.
> -
> -At least the following flags in `EFER` are guaranteed to be disabled:
> -
> -  * SCE (bit 0): System call extensions disabled.
> -  * NXE (bit 11): No-Execute disabled.
> -
> -There's no guarantee about the state of the other bits in the `EFER` 
> register.
> -
> -All the segments selectors are set with a flat base at zero.
> -
> -The `cs` segment selector attributes are set to 0x0a09b, which describes an
> -executable and readable code segment only accessible by the most privileged
> -level. The segment is also set as a 64-bit code segment (`L` flag set, `D` 
> flag
> -unset).
> -
> -The remaining segment selectors (`ds`, `ss`, `es`, `fs` and `gs`) are all set
> -to the same values. The attributes are set to 0x0c093, which implies a read 
> and
> -write data segment only accessible by the most privileged level.
> -
> -The `FS.base`, `GS.base` and `KERNEL_GS.base` MSRs are zeroed out.
> -
> -The `IDT` and `GDT` are also zeroed, so the guest must be specially careful 
> to
> -not trigger a fault until after they have been properly set. The way of 
> setting
> -the IDT and the GDT is using the native instructions as would be done on bare
> -metal.
> -
> -The `RFLAGS` register is guaranteed to be clear when jumping into the kernel
> -entry point, with the exception of the reserved bit 1 set.
> -
> -## Memory ##
> -
> -Since PVH guests rely on virtualization extensions provided by the CPU, they
> -have access to a hardware virtualized MMU, which means page-table related
> -operations should use the same instructions used on native.
> -
> -There are however some differences with native. The usage of native MTRR
> -operations is forbidden, and `XENPF_*_memtype` hypercalls should be used
> -instead. This can be avoided by simply not using MTRR and setting all the
> -memory attributes using PAT, which doesn't require the usage of any 
> hypercalls.
> -
> -Since PVH doesn't use a BIOS in order to boot, the physical memory map has
> -to be retrieved using the `XENMEM_memory_map` hypercall, which will return
> -an e820 map. This memory map might contain holes that describe MMIO regions,
> -that will be already setup by Xen.
> -
> -*TODO*: we need to figure out what to do with MMIO regions, right now Xen
> -sets all the holes in the native e820 to MMIO regions for Dom0 up to 4GB. We
> -need to decide what to do with MMIO regions above 4GB on Dom0, and what to do
> -for PVH DomUs with pci-passthrough.
> -
> -In the case of a guest started with memory != maxmem, the e820 memory map
> -returned by Xen will contain the memory up to maxmem. The guest has to be 
> very
> -careful to only use the lower memory pages up to the value contained in
> -`start_info->nr_pages` because any memory page above that value will not be
> -populated.
> -
> -## Physical devices ##
> -
> -When running as Dom0 the guest OS has the ability to interact with the 
> physical
> -devices present in the system. A note should be made that PVH guests require
> -a working IOMMU in order to interact with physical devices.
> -
> -The first step in order to manipulate the devices is to make Xen aware of
> -them. Due to the fact that all the hardware description on x86 comes from
> -ACPI, Dom0 is responsible for parsing the ACPI tables and notifying Xen about
> -the devices it finds. This is done with the `PHYSDEVOP_pci_device_add`
> -hypercall.
> -
> -*TODO*: explain the way to register the different kinds of PCI devices, like
> -devices with virtual functions.
> -
> -## Interrupts ##
> -
> -All interrupts on PVH guests are routed over event channels, see
> -[Event Channel Internals][event_channels] for more detailed information about
> -event channels. In order to inject interrupts into the guest an IDT vector is
> -used. This is the same mechanism used on PVHVM guests, and allows having
> -per-cpu interrupts that can be used to deliver timers or IPIs.
> -
> -In order to register the callback IDT vector the `HVMOP_set_param` hypercall
> -is used with the following values:
> -
> -    domid = DOMID_SELF
> -    index = HVM_PARAM_CALLBACK_IRQ
> -    value = (0x2 << 56) | vector_value
> -
> -The OS has to program the IDT for the `vector_value` using the baremetal
> -mechanism.
> -
> -In order to know which event channel has fired, we need to look into the
> -information provided in the `shared_info` structure. The `evtchn_pending`
> -array is used as a bitmap in order to find out which event channel has
> -fired. Event channels can also be masked by setting it's port value in the
> -`shared_info->evtchn_mask` bitmap.
> -
> -### Interrupts from physical devices ###
> -
> -When running as Dom0 (or when using pci-passthrough) interrupts from physical
> -devices are routed over event channels. There are 3 different kind of
> -physical interrupts that can be routed over event channels by Xen: IO APIC,
> -MSI and MSI-X interrupts.
> -
> -Since physical interrupts usually need EOI (End Of Interrupt), Xen allows the
> -registration of a memory region that will contain whether a physical 
> interrupt
> -needs EOI from the guest or not. This is done with the
> -`PHYSDEVOP_pirq_eoi_gmfn_v2` hypercall that takes a parameter containing the
> -physical address of the memory page that will act as a bitmap. Then in order 
> to
> -find out if an IRQ needs EOI or not, the OS can perform a simple bit test on 
> the
> -memory page using the PIRQ value.
> -
> -### IO APIC interrupt routing ###
> -
> -IO APIC interrupts can be routed over event channels using `PHYSDEVOP`
> -hypercalls. First the IRQ is registered using the `PHYSDEVOP_map_pirq`
> -hypercall, as an example IRQ#9 is used here:
> -
> -    domid = DOMID_SELF
> -    type = MAP_PIRQ_TYPE_GSI
> -    index = 9
> -    pirq = 9
> -
> -The IRQ#9 is now registered as PIRQ#9. The triggering and polarity can also
> -be configured using the `PHYSDEVOP_setup_gsi` hypercall:
> -
> -    gsi = 9 # This is the IRQ value.
> -    triggering = 0
> -    polarity = 0
> -
> -In this example the IRQ would be configured to use edge triggering and high
> -polarity.
> -
> -Finally the PIRQ can be bound to an event channel using the
> -`EVTCHNOP_bind_pirq`, that will return the event channel port the PIRQ has 
> been
> -assigned. After this the event channel will be ready for delivery.
> -
> -*NOTE*: when running as Dom0, the guest has to parse the interrupt overrides
> -found on the ACPI tables and notify Xen about them.
> -
> -### MSI ###
> -
> -In order to configure MSI interrupts for a device, Xen must be made aware of
> -it's presence first by using the `PHYSDEVOP_pci_device_add` as described 
> above.
> -Then the `PHYSDEVOP_map_pirq` hypercall is used:
> -
> -    domid = DOMID_SELF
> -    type = MAP_PIRQ_TYPE_MSI_SEG or MAP_PIRQ_TYPE_MULTI_MSI
> -    index = -1
> -    pirq = -1
> -    bus = pci_device_bus
> -    devfn = pci_device_function
> -    entry_nr = number of MSI interrupts
> -
> -The type has to be set to `MAP_PIRQ_TYPE_MSI_SEG` if only one MSI interrupt
> -source is being configured. On devices that support MSI interrupt groups
> -`MAP_PIRQ_TYPE_MULTI_MSI` can be used to configure them by also placing the
> -number of MSI interrupts in the `entry_nr` field.
> -
> -The values in the `bus` and `devfn` field should be the same as the ones used
> -when registering the device with `PHYSDEVOP_pci_device_add`.
> -
> -### MSI-X ###
> -
> -*TODO*: how to register/use them.
> -
> -## Event timers and timecounters ##
> -
> -Since some hardware is not available on PVH (like the local APIC), Xen 
> provides
> -the OS with suitable replacements in order to get the same functionality. One
> -of them is the timer interface. Using a set of hypercalls, a guest OS can set
> -event timers that will deliver and event channel interrupt to the guest.
> -
> -In order to use the timer provided by Xen the guest OS first needs to 
> register
> -a VIRQ event channel to be used by the timer to deliver the interrupts. The
> -event channel is registered using the `EVTCHNOP_bind_virq` hypercall, that
> -only takes two parameters:
> -
> -    virq = VIRQ_TIMER
> -    vcpu = vcpu_id
> -
> -The port that's going to be used by Xen in order to deliver the interrupt is
> -returned in the `port` field. Once the interrupt is set, the timer can be
> -programmed using the `VCPUOP_set_singleshot_timer` hypercall.
> -
> -    flags = VCPU_SSHOTTMR_future
> -    timeout_abs_ns = absolute value when the timer should fire
> -
> -It is important to notice that the `VCPUOP_set_singleshot_timer` hypercall 
> must
> -be executed from the same vCPU where the timer should fire, or else Xen will
> -refuse to set it. This is a single-shot timer, so it must be set by the OS
> -every time it fires if a periodic timer is desired.
> -
> -Xen also shares a memory region with the guest OS that contains time related
> -values that are updated periodically. This values can be used to implement a
> -timecounter or to obtain the current time. This information is placed inside 
> of
> -`shared_info->vcpu_info[vcpu_id].time`. The uptime (time since the guest has
> -been launched) can be calculated using the following expression and the 
> values
> -stored in the `vcpu_time_info` struct:
> -
> -    system_time + ((((tsc - tsc_timestamp) << tsc_shift) * 
> tsc_to_system_mul) >> 32)
> -
> -The timeout that is passed to `VCPUOP_set_singleshot_timer` has to be
> -calculated using the above value, plus the timeout the system wants to set.
> -
> -If the OS also wants to obtain the current wallclock time, the value 
> calculated
> -above has to be added to the values found in `shared_info->wc_sec` and
> -`shared_info->wc_nsec`.
> -
> -## SMP discover and bring up ##
> -
> -The process of bringing up secondary CPUs is obviously different from native,
> -since PVH doesn't have a local APIC. The first thing to do is to figure out
> -how many vCPUs the guest has. This is done using the `VCPUOP_is_up` 
> hypercall,
> -using for example this simple loop:
> -
> -    for (i = 0; i < MAXCPU; i++) {
> -        ret = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
> -        if (ret >= 0)
> -            /* vCPU#i is present */
> -    }
> -
> -Note than when running as Dom0, the ACPI tables might report a different 
> number
> -of available CPUs. This is because the value on the ACPI tables is the
> -number of physical CPUs the host has, and it might bear no resemblance with 
> the
> -number of vCPUs Dom0 actually has so it should be ignored.
> -
> -In order to bring up the secondary vCPUs they must be configured first. This 
> is
> -achieved using the `VCPUOP_initialise` hypercall. A valid context has to be
> -passed to the vCPU in order to boot. The relevant fields for PVH guests are
> -the following:
> -
> -  * `flags`: contains `VGCF_*` flags (see `arch-x86/xen.h` public header).
> -  * `user_regs`: struct that contains the register values that will be set on
> -    the vCPU before booting. All GPRs are available to be set, however, the
> -    most relevant ones are `rip` and `rsp` in order to set the start address
> -    and the stack. Please note, all selectors must be null.
> -  * `ctrlreg[3]`: contains the address of the page tables that will be used 
> by
> -    the vCPU. Other control registers should be set to zero, or else the
> -    hypercall will fail with -EINVAL.
> -
> -After the vCPU is initialized with the proper values, it can be started by
> -using the `VCPUOP_up` hypercall. The values of the other control registers of
> -the vCPU will be the same as the ones described in the `control registers`
> -section.
> -
> -Examples about how to bring up secondary CPUs can be found on the FreeBSD
> -code base in `sys/x86/xen/pv.c` and on Linux `arch/x86/xen/smp.c`.
> -
> -## Control operations (reboot/shutdown) ##
> -
> -Reboot and shutdown operations on PVH guests are performed using hypercalls.
> -In order to issue a reboot, a guest must use the `SHUTDOWN_reboot` hypercall.
> -In order to perform a power off from a guest DomU, the `SHUTDOWN_poweroff`
> -hypercall should be used.
> -
> -The way to perform a full system power off from Dom0 is different than what's
> -done in a DomU guest. In order to perform a power off from Dom0 the native
> -ACPI path should be followed, but the guest should not write the `SLP_EN`
> -bit to the Pm1Control register. Instead the `XENPF_enter_acpi_sleep` 
> hypercall
> -should be used, filling the following data in the `xen_platform_op` struct:
> -
> -    cmd = XENPF_enter_acpi_sleep
> -    interface_version = XENPF_INTERFACE_VERSION
> -    u.enter_acpi_sleep.pm1a_cnt_val = Pm1aControlValue
> -    u.enter_acpi_sleep.pm1b_cnt_val = Pm1bControlValue
> -
> -This will allow Xen to do it's clean up and to power off the system. If the
> -host is using hardware reduced ACPI, the following field should also be set:
> -
> -    u.enter_acpi_sleep.flags = XENPF_ACPI_SLEEP_EXTENDED (0x1)
> -
> -## CPUID ##
> -
> -The cpuid instruction that should be used is the normal `cpuid`, not the
> -emulated `cpuid` that PV guests usually require.
> -
> -*TDOD*: describe which cpuid flags a guest should ignore and also which flags
> -describe features can be used. It would also be good to describe the set of
> -cpuid flags that will always be present when running as PVH.
> -
> -## Final notes ##
> -
> -All the other hardware functionality not described in this document should be
> -assumed to be performed in the same way as native.
> -
> -[event_channels]: http://wiki.xen.org/wiki/Event_Channel_Internals
> -- 
> 2.11.0 (Apple Git-81)
> 

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