On 2/12/2025 3:25 PM, Easwar Hariharan wrote: > On 2/12/2025 3:01 PM, Nuno Das Neves wrote: >> On 2/11/2025 9:47 PM, Easwar Hariharan wrote: >>> On 2/11/2025 2:21 PM, Nuno Das Neves wrote: >>>> Introduce CONFIG_MSHV_ROOT as a tristate to enable root partition >>>> booting and future mshv driver functionality. >>>> >>>> Change hv_root_partition into a function which always returns false >>>> if CONFIG_MSHV_ROOT=n. >>>> >>>> Introduce hv_current_partition_type to store the type of partition >>>> (guest, root, or other kinds in future), and hv_identify_partition_type() >>>> to it up early in Hyper-V initialization. >>> >>> ...to *set* it up early? >>> >> Yep! Thanks for catching that >> >>>> >>>> Signed-off-by: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx> >>>> --- >>>> Depends on >>>> https://lore.kernel.org/linux-hyperv/1738955002-20821-3-git-send-email-nunodasneves@xxxxxxxxxxxxxxxxxxx/ >>>> >>>> arch/arm64/hyperv/mshyperv.c | 2 ++ >>>> arch/x86/hyperv/hv_init.c | 10 ++++---- >>>> arch/x86/kernel/cpu/mshyperv.c | 24 ++---------------- >>>> drivers/clocksource/hyperv_timer.c | 4 +-- >>>> drivers/hv/Kconfig | 12 +++++++++ >>>> drivers/hv/Makefile | 3 ++- >>>> drivers/hv/hv.c | 10 ++++---- >>>> drivers/hv/hv_common.c | 32 +++++++++++++++++++----- >>>> drivers/hv/vmbus_drv.c | 2 +- >>>> drivers/iommu/hyperv-iommu.c | 4 +-- >>>> include/asm-generic/mshyperv.h | 39 +++++++++++++++++++++++++----- >>>> 11 files changed, 92 insertions(+), 50 deletions(-) >>>> >>> >>> <snip> >>> >>>> + >>>> +void hv_identify_partition_type(void) >>>> +{ >>>> + /* >>>> + * Check partition creation and cpu management privileges >>>> + * >>>> + * Hyper-V should never specify running as root and as a Confidential >>>> + * VM. But to protect against a compromised/malicious Hyper-V trying >>>> + * to exploit root behavior to expose Confidential VM memory, ignore >>>> + * the root partition setting if also a Confidential VM. >>>> + */ >>>> + if ((ms_hyperv.priv_high & HV_CREATE_PARTITIONS) && >>>> + (ms_hyperv.priv_high & HV_CPU_MANAGEMENT) && >>>> + !(ms_hyperv.priv_high & HV_ISOLATION)) { >>>> + hv_current_partition_type = HV_PARTITION_TYPE_ROOT; >>>> + pr_info("Hyper-V: running as root partition\n"); >>>> + } else { >>>> + hv_current_partition_type = HV_PARTITION_TYPE_GUEST; >>>> + } >>>> +} >>> >>> This should assume GUEST as default and modify to ROOT if all the checks pass. >>> >> It is doing that, isn't it? >> >> In fact the 'else' branch here is redundant and just there for additional clarity. >> >> hv_current_partition_type is zeroed (so GUEST) by default, but I could make that explicit >> if you prefer: > > Yes, explicit is better, but see comment below. > >> +enum hv_partition_type hv_current_partition_type = HV_PARTITION_TYPE_GUEST; >> >> How does that sound? Am I misunderstanding something here? > > I'd suggest centralizing that in this function, instead of having it spread in 2 places. > Since your commit message hints at future partition types, it's ideal to have this function be > a central clearing house, which I suppose is the intent. The preferred pattern in general, and what I'm > suggesting, is something like this: > > void hv_identify_partition_type(void) > { > /* Assume guest role */ > hv_current_partition_type = HV_PARTITION_TYPE_GUEST; > > /* > * Check partition creation and cpu management privileges > * > * Hyper-V should never specify running as root and as a Confidential > * VM. But to protect against a compromised/malicious Hyper-V trying > * to exploit root behavior to expose Confidential VM memory, ignore > * the root partition setting if also a Confidential VM. > */ > if ((ms_hyperv.priv_high & HV_CREATE_PARTITIONS) && > (ms_hyperv.priv_high & HV_CPU_MANAGEMENT) && > !(ms_hyperv.priv_high & HV_ISOLATION)) { > hv_current_partition_type = HV_PARTITION_TYPE_ROOT; > pr_info("Hyper-V: running as root partition\n"); > } > } > Fair enough, happy to do it this way. >> >>> <snip> >>> >>>> +static inline int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages) >>>> +{ >>>> + return hv_result(U64_MAX); >>>> +} >>> >>> Is there value in perhaps #defining hv_result_<whatever this is> as U64_MAX and returning that for documentation? >>> For e.g. assuming this is something like EOPNOTSUPP >>> >>> #define HV_RESULT_NOT_SUPP U64_MAX >>> >>> static inline int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages) >>> { return hv_result(HV_RESULT_NOT_SUPP); } >>> >> The idea here was to copy what hv_do_hypercall does returning U64_MAX in case the hypercall >> page is missing, which will hv_result() into an invalid status code. A special value for >> that status could make this pattern clearer. > > Agreed, having a name for that status would be helpful, but we don't want to diverge too much from the hypervisor > definitions, especially if we're going to change it later again anyway. > >> I'd want to call out that this isn't a "real" >> Hyper-V status code somehow. HV_STATUS's are 16 bits, so it would look more like: >> >> /* "LINUX" because this isn't really a status from the hypervisor.. */ >> #define HV_STATUS_LINUX_FAIL 0xFFFF >> static inline int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages) >> { return HV_STATUS_LINUX_FAIL; } >> >> Another option: there is another patch coming (which you know of) which maps hypercall >> status codes to regular Linux errors like -EOPNOTSUPP. I could simply merge that patch >> with this one (or make this a series for v2), and that would result in less churn. >> (And leave alone the current use of U64_MAX in hv_do_hypercall, for now). >> > > I think that second option is a good idea. The hypervisor status should remain restricted to the functions that are > hv_do_hypercall() or call it directly, while the rest of the code uses standard errno values. I'd suggest making > it a series so each commit does 1 thing. > Ok I'll do that, thanks. Nuno > Thanks, > Easwar (he/him)
