Excerpts from Michael Ellerman's message of April 7, 2021 9:33 pm:

Nicholas Piggin [off-list ref] writes:

quoted

Starting with ISA v3.1, LPCR[AIL] no longer controls the interrupt
mode for HV=1 interrupts. Instead, a new LPCR[HAIL] bit is defined
which behaves like AIL=3 for HV interrupts when set.

Set HAIL on bare metal to give us mmu-on interrupts and improve
performance.

This also fixes an scv bug: we don't implement scv real mode (AIL=0)
vectors because they are at an inconvenient location, so we just
disable scv support when AIL can not be set. However powernv assumes
that LPCR[AIL] will enable AIL mode so it enables scv support despite
HV interrupts being AIL=0, which causes scv interrupts to go off into
the weeds.

Should we tag this as fixing the initial P10 support, or the scv
support? Or neither?

Good question. It does fix a nasty crash with scv so at least it should
be tagged I guess.

I don't know of anything else that assumes AIL on bare metal, so I don't 
know of a crashy bug it fixes with initial P10 support. But it is a bit 
odd for a HV OS running a v3.1 processor to set the old LPCR AIL bits, 
so it is some kind of bug fix (performance at least).

Could go either way I guess.

Thanks,
Nick

cheers

quoted

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 1be20bc8dce2..9086a2644c89 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h

@@ -441,6 +441,7 @@
 #define   LPCR_VRMA_LP1		ASM_CONST(0x0000800000000000)
 #define   LPCR_RMLS		0x1C000000	/* Implementation dependent RMO limit sel */
 #define   LPCR_RMLS_SH		26
+#define   LPCR_HAIL		ASM_CONST(0x0000000004000000)   /* HV AIL (ISAv3.1) */
 #define   LPCR_ILE		ASM_CONST(0x0000000002000000)   /* !HV irqs set MSR:LE */
 #define   LPCR_AIL		ASM_CONST(0x0000000001800000)	/* Alternate interrupt location */
 #define   LPCR_AIL_0		ASM_CONST(0x0000000000000000)	/* MMU off exception offset 0x0 */

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 04a31586f760..671192afcdfd 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c

@@ -233,10 +233,23 @@ static void cpu_ready_for_interrupts(void)
 	 * If we are not in hypervisor mode the job is done once for
 	 * the whole partition in configure_exceptions().
 	 */
-	if (cpu_has_feature(CPU_FTR_HVMODE) &&
-	    cpu_has_feature(CPU_FTR_ARCH_207S)) {
+	if (cpu_has_feature(CPU_FTR_HVMODE)) {
 		unsigned long lpcr = mfspr(SPRN_LPCR);
-		mtspr(SPRN_LPCR, lpcr | LPCR_AIL_3);
+		unsigned long new_lpcr = lpcr;
+
+		if (cpu_has_feature(CPU_FTR_ARCH_31)) {
+			/* P10 DD1 does not have HAIL */
+			if (pvr_version_is(PVR_POWER10) &&
+					(mfspr(SPRN_PVR) & 0xf00) == 0x100)
+				new_lpcr |= LPCR_AIL_3;
+			else
+				new_lpcr |= LPCR_HAIL;
+		} else if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
+			new_lpcr |= LPCR_AIL_3;
+		}
+
+		if (new_lpcr != lpcr)
+			mtspr(SPRN_LPCR, new_lpcr);
 	}
 
 	/*

-- 
2.23.0