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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] docs: remove PVHv1 document
commit 8ac9a25b26841b539fd7f345fc87a4142a86adb3
Author: Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Wed May 31 08:47:57 2017 +0200
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed May 31 08:47:57 2017 +0200
docs: remove PVHv1 document
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>
Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
docs/misc/pvh.markdown | 377 -------------------------------------------------
1 file changed, 377 deletions(-)
diff --git a/docs/misc/pvh.markdown b/docs/misc/pvh.markdown
deleted file mode 100644
index 52d8e74..0000000
--- 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
--
generated by git-patchbot for /home/xen/git/xen.git#master
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