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authorNicholas Piggin <npiggin@gmail.com>2022-02-22 07:47:25 +0100
committerMichael Ellerman <mpe@ellerman.id.au>2022-03-08 03:13:58 +0100
commitb5149e229218118c9cd44a4d256f970ddcbf745b (patch)
treeb9964eda915b74c8fbf66a1b3f73e942a30cc799 /arch/powerpc/kernel/exceptions-64s.S
parentMerge branch 'kvm-ppc-cap-210' of https://git.kernel.org/pub/scm/virt/kvm/kvm... (diff)
downloadlinux-b5149e229218118c9cd44a4d256f970ddcbf745b.tar.xz
linux-b5149e229218118c9cd44a4d256f970ddcbf745b.zip
KVM: PPC: Book3S PR: Disable SCV when AIL could be disabled
PR KVM does not support running with AIL enabled, and SCV does is not supported with AIL disabled. Fix this by ensuring the SCV facility is disabled with FSCR while a CPU could be running with AIL=0. The PowerNV host supports disabling AIL on a per-CPU basis, so SCV just needs to be disabled when a vCPU is being run. The pSeries machine can only switch AIL on a system-wide basis, so it must disable SCV support at boot if the configuration can potentially run a PR KVM guest. Also ensure a the FSCR[SCV] bit can not be enabled when emulating mtFSCR for the guest. SCV is not emulated for the PR guest at the moment, this just fixes the host crashes. Alternatives considered and rejected: - SCV support can not be disabled by PR KVM after boot, because it is advertised to userspace with HWCAP. - AIL can not be disabled on a per-CPU basis. At least when running on pseries it is a per-LPAR setting. - Support for real-mode SCV vectors will not be added because they are at 0x17000 so making such a large fixed head space causes immediate value limits to be exceeded, requiring a lot rework and more code. - Disabling SCV for any PR KVM possible kernel will cause a slowdown when not using PR KVM. - A boot time option to disable SCV to use PR KVM is user-hostile. - System call instruction emulation for SCV facility unavailable instructions is too complex and old emulation code was subtly broken and removed. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com> Link: https://lore.kernel.org/r/20220222064727.2314380-2-npiggin@gmail.com
Diffstat (limited to 'arch/powerpc/kernel/exceptions-64s.S')
-rw-r--r--arch/powerpc/kernel/exceptions-64s.S4
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 55caeee37c08..b66dd6f775a4 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -809,6 +809,10 @@ __start_interrupts:
* - MSR_EE|MSR_RI is clear (no reentrant exceptions)
* - Standard kernel environment is set up (stack, paca, etc)
*
+ * KVM:
+ * These interrupts do not elevate HV 0->1, so HV is not involved. PR KVM
+ * ensures that FSCR[SCV] is disabled whenever it has to force AIL off.
+ *
* Call convention:
*
* syscall register convention is in Documentation/powerpc/syscall64-abi.rst