Commit a8bf2fc4 authored by Mark Brown's avatar Mark Brown Committed by Will Deacon
Browse files

arm64/kpti: Move DAIF masking to C code 



We really don't want to take an exception while replacing TTBR1 so we mask
DAIF during the actual update. Currently this is done in the assembly
function idmap_cpu_replace_ttbr1() but it could equally be done in the only
caller of that function, cpu_replace_ttbr1(). This simplifies the assembly
code slightly and means that when working with the code around masking DAIF
flags there is one less piece of assembly code which needs to be considered.

While we're at it add a comment which makes explicit why we are masking
DAIF in this code.

There should be no functional effect.

Signed-off-by: default avatarMark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221123180209.634650-2-broonie@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 32d495b0

arch/arm64/include/asm/mmu_context.h

+10 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 


#include <asm/cacheflush.h>

#include <asm/cpufeature.h>

#include <asm/daifflags.h>

#include <asm/proc-fns.h>

#include <asm-generic/mm_hooks.h>

#include <asm/cputype.h>
@@ -152,6 +153,7 @@ static inline void cpu_replace_ttbr1(pgd_t *pgdp, pgd_t *idmap) 
	typedef void (ttbr_replace_func)(phys_addr_t);

	extern ttbr_replace_func idmap_cpu_replace_ttbr1;

	ttbr_replace_func *replace_phys;

	unsigned long daif;



	/* phys_to_ttbr() zeros lower 2 bits of ttbr with 52-bit PA */

	phys_addr_t ttbr1 = phys_to_ttbr(virt_to_phys(pgdp));
@@ -171,7 +173,15 @@ static inline void cpu_replace_ttbr1(pgd_t *pgdp, pgd_t *idmap) 
	replace_phys = (void *)__pa_symbol(idmap_cpu_replace_ttbr1);



	__cpu_install_idmap(idmap);



	/*

	 * We really don't want to take *any* exceptions while TTBR1 is

	 * in the process of being replaced so mask everything.

	 */

	daif = local_daif_save();

	replace_phys(ttbr1);

	local_daif_restore(daif);



	cpu_uninstall_idmap();

}

arch/arm64/mm/proc.S

+0 −4
Original line number Diff line number Diff line
@@ -189,16 +189,12 @@ SYM_FUNC_END(cpu_do_resume) 
 * called by anything else. It can only be executed from a TTBR0 mapping.

 */

SYM_TYPED_FUNC_START(idmap_cpu_replace_ttbr1)

	save_and_disable_daif flags=x2



	__idmap_cpu_set_reserved_ttbr1 x1, x3



	offset_ttbr1 x0, x3

	msr	ttbr1_el1, x0

	isb



	restore_daif x2



	ret

SYM_FUNC_END(idmap_cpu_replace_ttbr1)

	.popsection