From: Dave Martin <Dave.Martin@arm.com>
Date: Tue, 31 Oct 2017 15:51:18 +0000
Subject: arm64/sve: KVM: Hide SVE from CPU features exposed to guests
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Patch-mainline: v4.15-rc1
Git-commit: 07d79fe7c22364de34618e58b92a8f091bd7e03d
References: bsc#1077761

KVM guests cannot currently use SVE, because SVE is always
configured to trap to EL2.

However, a guest that sees SVE reported as present in
ID_AA64PFR0_EL1 may legitimately expect that SVE works and try to
use it.  Instead of working, the guest will receive an injected
undef exception, which may cause the guest to oops or go into a
spin.

To avoid misleading the guest into believing that SVE will work,
this patch masks out the SVE field from ID_AA64PFR0_EL1 when a
guest attempts to read this register.  No support is explicitly
added for ID_AA64ZFR0_EL1 either, so that is still emulated as
reading as zero, which is consistent with SVE not being
implemented.

This is a temporary measure, and will be removed in a later series
when full KVM support for SVE is implemented.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Alexander Graf <agraf@suse.de>
---
 arch/arm64/kvm/sys_regs.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -23,6 +23,7 @@
 #include <linux/bsearch.h>
 #include <linux/kvm_host.h>
 #include <linux/mm.h>
+#include <linux/printk.h>
 #include <linux/uaccess.h>
 
 #include <asm/cacheflush.h>
@@ -897,8 +898,17 @@
 {
 	u32 id = sys_reg((u32)r->Op0, (u32)r->Op1,
 			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
+	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
 
-	return raz ? 0 : read_sanitised_ftr_reg(id);
+	if (id == SYS_ID_AA64PFR0_EL1) {
+		if (val & (0xfUL << ID_AA64PFR0_SVE_SHIFT))
+			pr_err_once("kvm [%i]: SVE unsupported for guests, suppressing\n",
+				    task_pid_nr(current));
+
+		val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
+	}
+
+	return val;
 }
 
 /* cpufeature ID register access trap handlers */