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Re: [PATCH v2 3/3] xen/arm: Warn user on cpu errata 832075


On 28/10/2020 08:43, Bertrand Marquis wrote:

On 27 Oct 2020, at 22:44, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:

On Mon, 26 Oct 2020, Bertrand Marquis wrote:
When a Cortex A57 processor is affected by CPU errata 832075, a guest
not implementing the workaround for it could deadlock the system.
Add a warning during boot informing the user that only trusted guests
should be executed on the system.
An equivalent warning is already given to the user by KVM on cores
affected by this errata.

Also taint the hypervisor as unsecure when this errata applies and
mention Cortex A57 r0p0 - r1p2 as not security supported in SUPPORT.md

Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
SUPPORT.md               |  1 +
xen/arch/arm/cpuerrata.c | 13 +++++++++++++
2 files changed, 14 insertions(+)

diff --git a/SUPPORT.md b/SUPPORT.md
index 5fbe5fc444..f7a3b046b0 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -38,6 +38,7 @@ supported in this document.
### ARM v8

     Status: Supported
+    Status, Cortex A57 r0p0 - r1p2, not security supported (Errata 832075)

## Host hardware support

diff --git a/xen/arch/arm/cpuerrata.c b/xen/arch/arm/cpuerrata.c
index 0430069a84..b35e8cd0b9 100644
--- a/xen/arch/arm/cpuerrata.c
+++ b/xen/arch/arm/cpuerrata.c
@@ -503,6 +503,19 @@ void check_local_cpu_errata(void)
void __init enable_errata_workarounds(void)
+#ifdef CONFIG_ARM64_ERRATUM_832075
+    if ( cpus_have_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) )
+    {
+        printk_once("**** This CPU is affected by the errata 832075. ****\n"
+                    "**** Guests without CPU erratum workarounds     ****\n"
+                    "**** can deadlock the system!                   ****\n"
+                    "**** Only trusted guests should be used.        ****\n");

These can be on 2 lines, no need to be on 4 lines.

I can fix that in a v3.

I know that Julien wrote about printing the warning from
enable_errata_workarounds but to me it looks more natural if we did it
from the .enable function specific to ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE.

I have no preference either here but i kind of like this way because if we had 
more warnings
they would allow be at the same place.

So I add this placement in mind because the previous version was using warning_add() (It can't be called from non-init helper). As we are using printk_once() now, I don't really have a preference.

So I would stick with what you wrote.


Julien Grall



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