Patchwork [14/14] KVM: arm64: Clarify access behaviour for out-of-range SVE register slice IDs

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Submitter Dave Martin
Date April 12, 2019, 4:28 p.m.
Message ID <1555086498-26691-15-git-send-email-Dave.Martin@arm.com>
Download mbox | patch
Permalink /patch/772033/
State New
Headers show

Comments

Dave Martin - April 12, 2019, 4:28 p.m.
The existing documentation for which SVE register slice IDs are
considered out-of-range, and what happens when userspace tries to
access them, is cryptic.

This patch rewords the text with the aim of making it a bit easier to
understand.

No functional change.

Suggested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 Documentation/virtual/kvm/api.txt | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Patch

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 74c51c7..91cb12a 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2159,8 +2159,9 @@  arm64 SVE registers have the following bit patterns:
   0x6050 0000 0015 060 <slice:5>        FFR bits[256*slice + 255 : 256*slice]
   0x6060 0000 0015 ffff                 KVM_REG_ARM64_SVE_VLS pseudo-register
 
-Access to slices beyond the maximum vector length configured for the
-vcpu (i.e., where 16 * slice >= max_vq (**)) will fail with ENOENT.
+Access to register IDs where 2048 * slice >= 128 * max_vq will fail with
+ENOENT.  max_vq is the vcpu's maximum supported vector length in 128-bit
+quadwords: see (**) below.
 
 These registers are only accessible on vcpus for which SVE is enabled.
 See KVM_ARM_VCPU_INIT for details.