On 12/7/2024 6:59 PM, Michael Kelley wrote: > From: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx> Sent: Friday, December 6, 2024 2:22 PM >> >> There are several bits of Hyper-V-related code that today live in >> arch/x86 but are not really specific to x86_64 and will work on arm64 >> too. >> >> Some of these will be needed in the upcoming mshv driver code (for >> Linux as root partition on Hyper-V). > > Previously, Linux as the root partition on Hyper-V was x86 only, which is > why the code is currently under arch/x86. So evidently the mshv driver > is being expanded to support both x86 and arm64, correct? Assuming > that's the case, I have some thoughts about how the source code should > be organized and built. It's probably best to get this right to start with so > it doesn't need to be changed again. Yes, we plan on supporting both architectures (eventually). I completely agree that it's better to sort out these issues now rather than later. > > * Patch 2 of this series moves hv_call_deposit_pages() and > hv_call_create_vp() to common code, but does not move > hv_call_add_logical_proc(). All three are used together, so > I'm wondering why hv_call_add_logical_proc() isn't moved. > The only reason is that in our internal tree there's no common or arm64 code yet that uses it - there is no reason it can't also become common code! > * These three functions were originally put in a separate source > code file because of being specific to running in the root partition, > and not needed for generic Linux guest support. I think there's > value in keeping them in a separate file, rather than merging them > into hv_common.c. Maybe just move the entire hv_proc.c file? Agreed. I think it should be renamed too - this file will eventually contain some additional hypercall helper functions, some of which may also be shared by the driver code. Something like "hv_call_common.c"? > And then later, perhaps move the entire irqdomain.c file as well? Yes, may as well move it too. > There's also an interesting question of whether to move them into > drivers/hv, or create a new directory virt/hyperv. Hyper-V support > started out 15 years ago structured as a driver, hence "drivers/hv". > But over the time, the support has become significantly more than > just a driver, so "virt/hyperv" might be a better location for > non-driver code that had previously been under arch/x86 but is > now common to all architectures. > I'd be fine with using "virt/hyperv", but I thought "virt" was only for KVM. Another option would be to create subdirectories in "drivers/hv" to organize the different modules more cleanly (i.e. when the /dev/mshv driver code is introduced). > * Today, the code for running in the root partition is built along > with the rest of the Hyper-V support, and so is present in kernels > built for normal Linux guests on Hyper-V. I haven't thought about > all the implications, but perhaps there's value in having a CONFIG > option to build for the root partition, so that code can be dropped > from normal kernels. There's a significant amount of new code still > to come for mshv that could be excluded from normal guests in this > way. Also, the tests of the hv_root_partition variable could be > changed to a function the compiler detects is always "false" in a > kernel built without the CONFIG option, in which case it can drop > the code for where hv_root_partition is "true". > Using hv_root_partition is a good way to do it, since it won't require many #ifdefs or moving the existing code around too much. I can certainly give it a try, and create a separate patch series introducing the option. I suppose "CONFIG_HYPERV_ROOT" makes sense as a name? > * The code currently in hv_proc.c is built for x86 only, and validly > assumes the page size is 4K. But when the code moves to be > common across architectures, that assumption is no longer > valid in the general case. Perhaps the intent is that kernels for > the root partition should always be built with page size 4K on > arm64, but nothing enforces that intent. Personally, I think the code > should be made to work with page sizes other than 4K so as to not > leave technical debt. But I realize you may have other priorities. If > there were a CONFIG option for building for the root partition, > that option could be setup to enforce the 4K page size on arm64. > That makes sense. I suppose this can be done by selecting PAGE_SIZE_4KB under HYPERV in drivers/hv/Kconfig? I'm not how easy it will be to make the code work with different page sizes, since we use alloc_page() and similar in a few places, assuming 4k. Thanks Nuno > Anyway, thinking through these decisions up front could avoid > the need for additional moves later on. > > Michael > >> So this is a good time to move >> them to hv_common.c. >> >> Signed-off-by: Nuno Das Neves <nudasnev@xxxxxxxxxxxxx> >> >> Nuno Das Neves (2): >> hyperv: Move hv_current_partition_id to arch-generic code >> hyperv: Move create_vp and deposit_pages hvcalls to hv_common.c >> >> arch/arm64/hyperv/mshyperv.c | 3 + >> arch/x86/hyperv/hv_init.c | 25 +---- >> arch/x86/hyperv/hv_proc.c | 144 --------------------------- >> arch/x86/include/asm/mshyperv.h | 4 - >> drivers/hv/hv_common.c | 168 ++++++++++++++++++++++++++++++++ >> include/asm-generic/mshyperv.h | 4 + >> 6 files changed, 176 insertions(+), 172 deletions(-) >> >> -- >> 2.34.1
