[PATCH v3 0/1] x86/vmware: Share steal-time counters in encrypted guests

[Zack Rusin <zack.rusin@broadcom.com>]

Steal time is the time a virtual CPU was ready to run but waited for the
host to schedule it. For example, in a 100 ms interval a vCPU might run
for 70 ms and wait 30 ms for a physical CPU. Reporting those 30 ms lets
Linux:
- account CPU usage accurately, without charging applications for time
  their vCPU wasn't running;
- base scheduling decisions on the CPU time tasks actually received;
- show host contention in the "st" column of top and vmstat and in
  /proc/stat.

VMware writes a running total into a small per-CPU buffer in guest
memory, and Linux reads it. In a confidential guest (AMD SEV-SNP, Intel
TDX) memory is private by default and the host cannot write it, so the
guest has to share the buffer first. Linux currently registers the
buffer without sharing it, and ESXi then powers off the VM. This only
affects VMs with the steal clock enabled, which ESXi enables by default
only for Photon guests.

Following the v2 discussion, this version uses one packed allocation for
all possible CPUs' counters and shares it before registering any address.
Setup moves to an early initcall so it can use the normal memory-conversion
API. This avoids converting a page in every CPU's per-CPU area and
concentrates sharing in one allocation.

Changes since v2:
- Replace the six infrastructure patches with one VMware-only fix.
- Leave the per-CPU allocator, linker, KVM and early conversion code alone.
- Move ordinary-guest setup to the same initcall.
- Rebase onto v7.3.

Tested on ordinary VMware x86-64 SMP/UP guests, ESXi SEV-SNP and TDX
guests (SMP, UP, 66 vCPUs and percpu_alloc=page), and QEMU/KVM x86-64
guests.

v2: https://lore.kernel.org/r/20260929040256.543767-1-zack.rusin@broadcom.com

Zack Rusin (1):
  x86/vmware: Allocate shared storage for steal-time counters

 arch/x86/kernel/cpu/vmware.c | 130 +++++++++++++++++++++++------------
 1 file changed, 86 insertions(+), 44 deletions(-)


base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222