Re: [PATCH v3 4/6] KVM: PPC: Book3s HV: Hold LPIDs in an unsigned long

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On 14/8/23 6:15 pm, David Laight wrote:
From: Jordan Niethe
Sent: 07 August 2023 02:46

The LPID register is 32 bits long. The host keeps the lpids for each
guest in an unsigned word struct kvm_arch. Currently, LPIDs are already
limited by mmu_lpid_bits and KVM_MAX_NESTED_GUESTS_SHIFT.

The nestedv2 API returns a 64 bit "Guest ID" to be used be the L1 host
for each L2 guest. This value is used as an lpid, e.g. it is the
parameter used by H_RPT_INVALIDATE. To minimize needless special casing
it makes sense to keep this "Guest ID" in struct kvm_arch::lpid.

This means that struct kvm_arch::lpid is too small so prepare for this
and make it an unsigned long. This is not a problem for the KVM-HV and
nestedv1 cases as their lpid values are already limited to valid ranges
so in those contexts the lpid can be used as an unsigned word safely as

Shouldn't it be changed to u64?

This will only be for 64-bit PPC so an unsigned long will always be 64 bits wide, but I can use a u64 instead.

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