[RESEND PATCH] arm64: Add support for VMID aware PIPT instruction cache

[RESEND PATCH] arm64: Add support for VMID aware PIPT instruction cache

[Shanker Donthineni]

In ARMv8.2 extension, a new instruction cache type 'VMID aware
PIPT' was introduced in addition to AIVIVT/VIPT/PIPT. Instruction
cache maintenance operations when issued from Non-secure EL1/EL0
have an effect only on cache line entries those were fetched in
Non-secure EL1/EL0 using the current VMID. For software point of
view, this cache type is same as PIPT and no aliasing problem.

The updated CTR_EL0.L1IP definition.
   00: VMID aware PIPT
   01: ASID-tagged Virtual Index, Virtual Tag (AIVIVT)
   10: Virtual Index, Physical Tag (VIPT)
   11: Physical Index, Physical Tag (PIPT)

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
---
 arch/arm64/include/asm/cachetype.h | 2 +-
 arch/arm64/kernel/cpuinfo.c        | 9 +++++----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/cachetype.h b/arch/arm64/include/asm/cachetype.h
index f05974c..cb84b4d 100644
--- a/arch/arm64/include/asm/cachetype.h
+++ b/arch/arm64/include/asm/cachetype.h
@@ -23,7 +23,7 @@
 #define CTR_CWG_SHIFT		24
 #define CTR_CWG_MASK		15
 
-#define ICACHE_POLICY_RESERVED	0
+#define ICACHE_POLICY_VPIPT	0
 #define ICACHE_POLICY_AIVIVT	1
 #define ICACHE_POLICY_VIPT	2
 #define ICACHE_POLICY_PIPT	3
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 2d52f8d..e2063de 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -43,7 +43,7 @@
 static struct cpuinfo_arm64 boot_cpu_data;
 
 static char *icache_policy_str[] = {
-	[ICACHE_POLICY_RESERVED] = "RESERVED/UNKNOWN",
+	[ICACHE_POLICY_VPIPT] = "VPIPT",
 	[ICACHE_POLICY_AIVIVT] = "AIVIVT",
 	[ICACHE_POLICY_VIPT] = "VIPT",
 	[ICACHE_POLICY_PIPT] = "PIPT",
@@ -288,7 +288,7 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
 	unsigned int cpu = smp_processor_id();
 	u32 l1ip = CTR_L1IP(info->reg_ctr);
 
-	if (l1ip != ICACHE_POLICY_PIPT) {
+	if (l1ip == ICACHE_POLICY_AIVIVT || l1ip == ICACHE_POLICY_VIPT) {
 		/*
 		 * VIPT caches are non-aliasing if the VA always equals the PA
 		 * in all bit positions that are covered by the index. This is
@@ -299,9 +299,10 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
 
 		if (l1ip != ICACHE_POLICY_VIPT || waysize > PAGE_SIZE)
 			set_bit(ICACHEF_ALIASING, &__icache_flags);
+
+		if (l1ip == ICACHE_POLICY_AIVIVT)
+			set_bit(ICACHEF_AIVIVT, &__icache_flags);
 	}
-	if (l1ip == ICACHE_POLICY_AIVIVT)
-		set_bit(ICACHEF_AIVIVT, &__icache_flags);
 
 	pr_info("Detected %s I-cache on CPU%d\n", icache_policy_str[l1ip], cpu);
 }
-- 
Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [RESEND PATCH] arm64: Add support for VMID aware PIPT instruction cache

[Will Deacon]

Hi Shanker,

Sorry for the delay in responding to this -- the patch isn't as
straightforward as it looks.

On Tue, Feb 21, 2017 at 08:09:55AM -0600, Shanker Donthineni wrote:
> In ARMv8.2 extension, a new instruction cache type 'VMID aware
> PIPT' was introduced in addition to AIVIVT/VIPT/PIPT. Instruction
> cache maintenance operations when issued from Non-secure EL1/EL0
> have an effect only on cache line entries those were fetched in
> Non-secure EL1/EL0 using the current VMID. For software point of
> view, this cache type is same as PIPT and no aliasing problem.

This may well cause problems for KVM with non-VHE, because the host VMID
is different from the guest VMID, yet we assume that I-cache invalidation
by the host *will* affect the guest when, for example, invalidating the
I-cache for pages holding the guest kernel Image.

I have some patches to address this (and some other bits in this area), so
I'll polish them off and post them shortly. Given that we're in the merge
window and this is 4.12 material, it's not urgent.

Will