(+ Marc) On Tue, 22 Feb 2022 at 03:42, Ashish Singhal <ashishsin...@nvidia.com> wrote: > > Even with MMU turned off, instruction cache can speculate > and fetch instructions. This can cause a crash if region > being executed has been modified recently. With this patch, > we ensure that instruction cache is invalidated right after > MMU has been enabled and any potentially stale instruction > fetched earlier has been discarded. >
I don't follow this reasoning. Every time the UEFI image loader loads an image into memory, it does so with MMU and caches enabled, and the code regions are cleaned to the PoU before being invalidated in the I-cache. So how could these regions be stale? The only code that needs special care here is the little trampoline that executes with the MMU off, but this is being taken care of explicitly, by cleaning the code to the PoC before invoking it. > This is specially helpful when the memory attributes of a > region in MMU are being changed and some instructions > operating on the region are prefetched in the instruction > cache. > This sounds like a TLB problem not a cache problem. For the sake of posterity, could you include a more detailed description of the issue in the commit log? IIRC, this is about speculative instruction fetches hitting device memory locations? As I mentioned before, the architecture does not permit speculative instruction fetches for regions mapped with the XN attribute. Is the issue occurring under virtualization? Is there a stage 2 mapping that lacks the XN attribute for the device memory region in question? > Signed-off-by: Ashish Singhal <ashishsin...@nvidia.com> > --- > ArmPkg/Library/ArmLib/AArch64/AArch64Support.S | 4 +++- > ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S | 2 ++ > 2 files changed, 5 insertions(+), 1 deletion(-) > > diff --git a/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S > b/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S > index d3cc1e8671..9648245182 100644 > --- a/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S > +++ b/ArmPkg/Library/ArmLib/AArch64/AArch64Support.S > @@ -89,7 +89,9 @@ ASM_FUNC(ArmEnableMmu) > dsb nsh > isb > msr sctlr_el3, x0 // Write back > -4: isb > +4: ic iallu > + dsb sy > + isb > ret > > > diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S > b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S > index 66ebca571e..56cc2dd73f 100644 > --- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S > +++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S > @@ -37,6 +37,8 @@ > > // re-enable the MMU > msr sctlr_el\el, x8 > + ic iallu > + dsb sy > isb > .endm > > -- > 2.17.1 > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#86883): https://edk2.groups.io/g/devel/message/86883 Mute This Topic: https://groups.io/mt/89309504/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
