linux-kernel - [PATCH 4/4] KVM: arm64: show writable masks for feature registers

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Date: Fri,  5 Apr 2024 14:01:08 +0200
From: Sebastian Ott <sebott@...hat.com>
To: linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Cc: Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Subject: [PATCH 4/4] KVM: arm64: show writable masks for feature registers

Instead of using ~0UL provide the actual writable mask for
non-id feature registers in the output of the
KVM_ARM_GET_REG_WRITABLE_MASKS ioctl.

Explicitely set the mask for CLIDR_EL1 to make sure we present
the same value to userspace than before.

This changes the mask for the CTR_EL0 register in the output
of the KVM_ARM_GET_REG_WRITABLE_MASKS ioctl.

Signed-off-by: Sebastian Ott <sebott@...hat.com>
---
 arch/arm64/kvm/sys_regs.c | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index b0ba292259f9..947aa9c0784f 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2505,7 +2505,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 
 	{ SYS_DESC(SYS_CCSIDR_EL1), access_ccsidr },
 	{ SYS_DESC(SYS_CLIDR_EL1), access_clidr, reset_clidr, CLIDR_EL1,
-	  .set_user = set_clidr },
+	  .set_user = set_clidr, .val = ~0UL },
 	{ SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
 	{ SYS_DESC(SYS_SMIDR_EL1), undef_access },
 	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
@@ -4059,20 +4059,11 @@ int kvm_vm_ioctl_get_reg_writable_masks(struct kvm *kvm, struct reg_mask_range *
 		if (!is_feature_id_reg(encoding) || !reg->set_user)
 			continue;
 
-		/*
-		 * For ID registers, we return the writable mask. Other feature
-		 * registers return a full 64bit mask. That's not necessary
-		 * compliant with a given revision of the architecture, but the
-		 * RES0/RES1 definitions allow us to do that.
-		 */
-		if (is_id_reg(encoding)) {
-			if (!reg->val ||
-			    (is_aa32_id_reg(encoding) && !kvm_supports_32bit_el0()))
-				continue;
-			val = reg->val;
-		} else {
-			val = ~0UL;
+		if (!reg->val ||
+		    (is_aa32_id_reg(encoding) && !kvm_supports_32bit_el0())) {
+			continue;
 		}
+		val = reg->val;
 
 		if (put_user(val, (masks + KVM_ARM_FEATURE_ID_RANGE_INDEX(encoding))))
 			return -EFAULT;
-- 
2.42.0