4e3fa1ae - powerpc/vdso: Implement __arch_get_vdso_rng_data()

Wed, 02 Oct 2024 08:39:29 +0000

powerpc/vdso: Implement __arch_get_vdso_rng_data()VDSO time functions do not call any other function, so they don'tneed to save/restore LR. However, retrieving the address of VDSO datapage requires using LR hence saving then restoring it, which can beheavy on some CPUs. On the other hand, VDSO functions on powerpc arenot standard functions and require a wrapper function to call C VDSOfunctions. And that wrapper has to save and restore LR in order tocall the C VDSO function, so retrieving VDSO data page address in thatwrapper doesn't require additional save/restore of LR.For random VDSO functions it is a bit different. Because the functioncalls __arch_chacha20_blocks_nostack(), it saves and restores LR.Retrieving VDSO data page address can then be done there withoutadditional save/restore of LR.So lets implement __arch_get_vdso_rng_data() and simplify the wrapper.It starts paving the way for the day powerpc will implement a morestandard ABI for VDSO functions.Signed-off-by: Christophe Leroy Signed-off-by: Michael Ellerman Link: https://patch.msgid.link/a1a9bd0df508f1b5c04684b7366940577dfc6262.1727858295.git.christophe.leroy@csgroup.eu List of files: /linux-6.15/arch/powerpc/kernel/vdso/vgetrandom.c

53cee505 - powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32

Mon, 02 Sep 2024 19:17:21 +0000

powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32To be consistent with other VDSO functions, the function is called__kernel_getrandom()__arch_chacha20_blocks_nostack() fonction is implemented basicallywith 32 bits operations. It performs 4 QUARTERROUND operations inparallele. There are enough registers to avoid using the stack:On input: r3: output bytes r4: 32-byte key input r5: 8-byte counter input/output r6: number of 64-byte blocks to write to outputDuring operation: stack: pointer to counter (r5) and non-volatile registers (r14-131) r0: counter of blocks (initialised with r6) r4: Value '4' after key has been read, used for indexing r5-r12: key r14-r15: block counter r16-r31: chacha stateAt the end: r0, r6-r12: Zeroised r5, r14-r31: RestoredPerformance on powerpc 885 (using kernel selftest): ~# ./vdso_test_getrandom bench-single vdso: 25000000 times in 62.938002291 seconds libc: 25000000 times in 535.581916866 seconds syscall: 25000000 times in 531.525042806 secondsPerformance on powerpc 8321 (using kernel selftest): ~# ./vdso_test_getrandom bench-single vdso: 25000000 times in 16.899318858 seconds libc: 25000000 times in 131.050596522 seconds syscall: 25000000 times in 129.794790389 secondsThis first patch adds support for VDSO32. As selftests cannot easilybe generated only for VDSO32, and because the following patch bringssupport for VDSO64 anyway, this patch opts out all code in__arch_chacha20_blocks_nostack() so that vdso_test_chacha will notfail to compile and will not crash on PPC64/PPC64LE, allthough theselftest itself will fail.Signed-off-by: Christophe Leroy Acked-by: Michael Ellerman Signed-off-by: Jason A. Donenfeld List of files: /linux-6.15/arch/powerpc/kernel/vdso/vgetrandom.c

Changes in vgetrandom.c

4e3fa1ae - powerpc/vdso: Implement __arch_get_vdso_rng_data()

53cee505 - powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32