From cfa7ff959a789a953eac40c8ac793e2cfc2db931 Mon Sep 17 00:00:00 2001 From: Mark Brown Date: Thu, 3 Jun 2021 19:41:18 +0100 Subject: arm64: smccc: Support SMCCC v1.3 SVE register saving hint SMCCC v1.2 requires that all SVE state be preserved over SMC calls which introduces substantial overhead in the common case where there is no SVE state in the registers. To avoid this SMCCC v1.3 introduces a flag which allows the caller to say that there is no state that needs to be preserved in the registers. Make use of this flag, setting it if the SMCCC version indicates support for it and the TIF_ flags indicate that there is no live SVE state in the registers, this avoids placing any constraints on when SMCCC calls can be done or triggering extra saving and reloading of SVE register state in the kernel. This would be straightforward enough except for the rather entertaining inline assembly we use to do SMCCC v1.1 calls to allow us to take advantage of the limited number of registers it clobbers. Deal with this by having a function which we call immediately before issuing the SMCCC call to make our checks and set the flag. Using alternatives the overhead if SVE is supported but not detected at runtime can be reduced to a single NOP. Signed-off-by: Mark Brown Reviewed-by: Ard Biesheuvel Reviewed-by: Marc Zyngier Link: https://lore.kernel.org/r/20210603184118.15090-1-broonie@kernel.org Signed-off-by: Will Deacon --- drivers/firmware/smccc/smccc.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'drivers/firmware') diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c index 028f81d702cc..9f937b125ab0 100644 --- a/drivers/firmware/smccc/smccc.c +++ b/drivers/firmware/smccc/smccc.c @@ -15,6 +15,7 @@ static u32 smccc_version = ARM_SMCCC_VERSION_1_0; static enum arm_smccc_conduit smccc_conduit = SMCCC_CONDUIT_NONE; bool __ro_after_init smccc_trng_available = false; +u64 __ro_after_init smccc_has_sve_hint = false; void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit) { @@ -22,6 +23,9 @@ void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit) smccc_conduit = conduit; smccc_trng_available = smccc_probe_trng(); + if (IS_ENABLED(CONFIG_ARM64_SVE) && + smccc_version >= ARM_SMCCC_VERSION_1_3) + smccc_has_sve_hint = true; } enum arm_smccc_conduit arm_smccc_1_1_get_conduit(void) -- cgit v1.2.3