On 7/17/2025 9:55 PM, mhkelle...@gmail.com wrote: > From: Michael Kelley <mhkli...@outlook.com> > > This patch set introduces a new way to manage the use of the per-vCPU > memory that is usually the input and output arguments to Hyper-V > hypercalls. Current code allocates the "hyperv_pcpu_input_arg", and in > some configurations, the "hyperv_pcpu_output_arg". Each is a 4 KiB > page of memory allocated per-vCPU. A hypercall call site disables > interrupts, then uses this memory to set up the input parameters for > the hypercall, read the output results after hypercall execution, and > re-enable interrupts. The open coding of these steps has led to > inconsistencies, and in some cases, violation of the generic > requirements for the hypercall input and output as described in the > Hyper-V Top Level Functional Spec (TLFS)[1]. This patch set introduces > a new family of inline functions to replace the open coding. The new > functions encapsulate key aspects of the use of per-vCPU memory for > hypercall input and output, and ensure that the TLFS requirements are > met (max size of 1 page each for input and output, no overlap of input > and output, aligned to 8 bytes, etc.). > > With this change, hypercall call sites no longer directly access > "hyperv_pcpu_input_arg" and "hyperv_pcpu_output_arg". Instead, one of > a family of new functions provides the per-vCPU memory that a hypercall > call site uses to set up hypercall input and output areas. > Conceptually, there is no longer a difference between the "per-vCPU > input page" and "per-vCPU output page". Only a single per-vCPU page is > allocated, and it is used to provide both hypercall input and output. > All current hypercalls can fit their input and output within that single > page, though the new code allows easy changing to two pages should a > future hypercall require a full page for each of the input and output. > > The new functions always zero the fixed-size portion of the hypercall > input area (but not any array portion -- see below) so that > uninitialized memory isn't inadvertently passed to the hypercall. > Current open-coded hypercall call sites are inconsistent on this point, > and use of the new functions addresses that inconsistency. The output > area is not zero'ed by the new code as it is Hyper-V's responsibility > to provide legal output. > > When the input or output (or both) contain an array, the new code > calculates and returns how many array entries fit within the per-vCPU > memory page, which is effectively the "batch size" for the hypercall > processing multiple entries. This batch size can then be used in the > hypercall control word to specify the repetition count. This > calculation of the batch size replaces current open coding of the > batch size, which is prone to errors. Note that the array portion of > the input area is *not* zero'ed. The arrays are almost always 64-bit > GPAs or something similar, and zero'ing that much memory seems > wasteful at runtime when it will all be overwritten. The hypercall > call site is responsible for ensuring that no part of the array is > left uninitialized (just as with current code). > > The new family of functions is realized as a single inline function > that handles the most complex case, which is a hypercall with input > and output, both of which contain arrays. Simpler cases are mapped to > this most complex case with #define wrappers that provide zero or NULL > for some arguments. Several of the arguments to this new function > must be compile-time constants generated by "sizeof()" expressions. > As such, most of the code in the new function is evaluated by the > compiler, with the result that the runtime code paths are no longer > than with the current open coding. An exception is the new code > generated to zero the fixed-size portion of the input area in cases > where it was not previously done. > > Use of the new function typically (but not always) saves a few lines > of code at each hypercall call site. This is traded off against the > lines of code added for the new functions. With code currently > upstream, the net is an add of about 20 lines of code and comments. > > A couple hypercall call sites have requirements that are not 100% > handled by the new function. These still require some manual open- > coded adjustment or open-coded batch size calculations -- see the > individual patches in this series. Suggestions on how to do better > are welcome. > > The patches in the series do the following: > > Patch 1: Introduce the new family of functions for assigning hypercall > input and output arguments. > > Patch 2 to 6: Change existing hypercall call sites to use one of the new > functions. In some cases, tweaks to the hypercall argument data > structures are necessary, but these tweaks are making the data > structures more consistent with the overall pattern. These > 5 patches are independent of each other, and can go in any > order. The breakup into 5 patches is for ease of review. > > Patch 7: Update the name of the variable used to hold the per-vCPU memory > used for hypercall arguments. Remove code for managing the > per-vCPU output page. > > The new code compiles and runs successfully on x86 and arm64. However, > basic smoke tests cover only a limited number of hypercall call sites > that have been modified. I don't have the hardware or Hyper-V > configurations needed to test running in the Hyper-V root partition > or running in a VTL other than VTL 0. The related hypercall call sites > still need to be tested to make sure I didn't break anything. Hopefully > someone with the necessary configurations and Hyper-V versions can > help with that testing. > > For gcc 9.4.0, I've looked at the generated code for a couple of > hypercall call sites on both x86 and arm64 to ensure that it boils > down to the equivalent of the current open coding. I have not looked > at the generated code for later gcc versions or for Clang/LLVM, but > there's no reason to expect something worse as the code isn't doing > anything tricky. > > This patch set is built against linux-next20250716. > > [1] > https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/tlfs > > Michael Kelley (7): > Drivers: hv: Introduce hv_setup_*() functions for hypercall arguments > x86/hyperv: Use hv_setup_*() to set up hypercall arguments -- part 1 > x86/hyperv: Use hv_setup_*() to set up hypercall arguments -- part 2 > Drivers: hv: Use hv_setup_*() to set up hypercall arguments > PCI: hv: Use hv_setup_*() to set up hypercall arguments > Drivers: hv: Use hv_setup_*() to set up hypercall arguments for mshv > code > Drivers: hv: Replace hyperv_pcpu_input/output_arg with hyperv_pcpu_arg > > arch/x86/hyperv/hv_apic.c | 10 +-- > arch/x86/hyperv/hv_init.c | 12 ++- > arch/x86/hyperv/hv_vtl.c | 3 +- > arch/x86/hyperv/irqdomain.c | 17 ++-- > arch/x86/hyperv/ivm.c | 18 ++--- > arch/x86/hyperv/mmu.c | 19 ++--- > arch/x86/hyperv/nested.c | 14 ++-- > drivers/hv/hv.c | 6 +- > drivers/hv/hv_balloon.c | 8 +- > drivers/hv/hv_common.c | 64 +++++---------- > drivers/hv/hv_proc.c | 23 +++--- > drivers/hv/hyperv_vmbus.h | 2 +- > drivers/hv/mshv_common.c | 31 +++---- > drivers/hv/mshv_root_hv_call.c | 121 +++++++++++----------------- > drivers/hv/mshv_root_main.c | 5 +- > drivers/pci/controller/pci-hyperv.c | 18 ++--- > include/asm-generic/mshyperv.h | 106 +++++++++++++++++++++++- > include/hyperv/hvgdk_mini.h | 4 +- > 18 files changed, 251 insertions(+), 230 deletions(-) >
Thank you for spinning this version! For the series, Reviewed-by: Easwar Hariharan <eahar...@linux.microsoft.com>
