On 08/12/2020 14:38, Bertrand Marquis wrote:
Hi Julien,
On 8 Dec 2020, at 09:47, Julien Grall <[email protected]> wrote:
Hi,
On 08/12/2020 07:23, Michal Orzel wrote:
When executing in aarch32 state at EL0, a load at EL0 from a
virtual address that matches the bottom 32 bits of the virtual address
used by a recent load at (aarch64) EL1 might return incorrect data.
The workaround is to insert a write of the contextidr_el1 register
on exception return to an aarch32 guest.
I am a bit confused with this comment. In the previous paragraph, you are
suggesting that the problem is an interaction between EL1 AArch64 and EL0
AArch32. But here you seem to imply the issue only happen when running a
AArch32 guest.
Can you clarify it?
This can happen when switching from an aarch64 guest to an aarch32 guest so not
only when there is interaction.
Right, but the context switch will write to CONTEXTIDR_EL1. So this case
should already be handled.
Xen will never switch from AArch64 EL1 to AArch32 EL0 without a context
switch (the inverse can happen if we inject an exception to the guest).
Reading the Cortex-A53 SDEN, it sounds like this is an OS and not
Hypervisor problem. In fact, Linux only seems to workaround it when
switching in the OS side rather than the hypervisor.
Therefore, I am not sure to understand why we need to workaroud it in Xen.
Cheers,
--
Julien Grall
