From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Tue, 17 Nov 2015 17:17:09 +0000 Subject: [RFC PATCH] arm64: use non-global mappings for UEFI runtime regions In-Reply-To: References: <1447750411-6424-1-git-send-email-ard.biesheuvel@linaro.org> <20151117152558.GK12586@leverpostej> <20151117163445.GE30101@arm.com> <20151117164759.GA12266@leverpostej> Message-ID: <20151117171709.GB12266@leverpostej> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > >> > For backporting, I'm not sure that this is necessarily safe prior to > >> > Will's rework of the ASID allocator. I think we can IPI in this context, > >> > and it looks like the cpu_set_reserved_ttbr0() in flush_context() would > >> > save us from the problem described above, but I may have missed > >> > something. > >> > > >> > Will, are you aware of anything that could bite us here? > >> > >> Can we guarantee that efi_virtmap_{load,unload} are called with interrupts > >> enabled? > > > > Unfortuantely, it looks like we can guarantee interrupts are _disabled_. > > > > Every function in drivers/firmware/efi/runtime-wrappers.c which uses > > efi_call_virt (and hence efi_virtmap_{load,unload}) wraps the call in a > > spin_lock_irq{save,restore} pair. Those appear to be the only uses of > > efi_call_virt. > > > > There is actually no need from the UEFI pov to invoke the UEFI runtime > services with interrupts disabled, this is simply an implementation > detail of the kernel support, and I think it is primarily for x86 (but > I have to dig up the old thread for the details) > > And even if we stick with spin_lock_irqsave(), we could refactor the > runtime wrappers to perform the mm switch outside of them. Ok. I'm only thinking about stable here. In the context of a stable backport, I think the simplest thing to do is always go via the resesrved ttbr0 to perform the TLB flush, and hand-code the save/restore of the active mm's TTBR0_EL1 value rather than going through cpu_switch_mm (which I believe we can't call with interrupts disabled). It doesn't look like it's easy to stash the value given efi_virtmap_{load,unload} are separate functions, and I don't think we can just restore from current->active_mm in case there was a concurrent rollover on another CPU. Mark.