On Thu, Apr 18, 2024 at 08:52:56AM -0700, Eric Biggers wrote: > Hi Conor, > > On Thu, Apr 18, 2024 at 12:02:10PM +0100, Conor Dooley wrote: > > +CC Eric, Jerry > > > > On Fri, Apr 12, 2024 at 02:49:03PM +0800, Andy Chiu wrote: > > > Make has_vector take one argument. This argument represents the minimum > > > Vector subextension that the following Vector actions assume. > > > > > > Also, change riscv_v_first_use_handler(), and boot code that calls > > > riscv_v_setup_vsize() to accept the minimum Vector sub-extension, > > > ZVE32X. > > > > > > Most kernel/user interfaces requires minimum of ZVE32X. Thus, programs > > > compiled and run with ZVE32X should be supported by the kernel on most > > > aspects. This includes context-switch, signal, ptrace, prctl, and > > > hwprobe. > > > > > > One exception is that ELF_HWCAP returns 'V' only if full V is supported > > > on the platform. This means that the system without a full V must not > > > rely on ELF_HWCAP to tell whether it is allowable to execute Vector > > > without first invoking a prctl() check. > > > > > > Signed-off-by: Andy Chiu <andy.chiu@xxxxxxxxxx> > > > Acked-by: Joel Granados <j.granados@xxxxxxxxxxx> > > > > I'm not sure that I like this patch to be honest. As far as I can tell, > > every user here of has_vector(ext) is ZVE32X, so why bother actually > > having an argument? > > > > Could we just document that has_vector() is just a tyre kick of "is > > there a vector unit and are we allowed to use it", and anything > > requiring more than the bare-minimum (so zve32x?)must explicitly check > > for that form of vector using riscv_has_extension_[un]likely()? > > > > Finally, the in-kernel crypto stuff or other things that use > > can_use_simd() to check for vector support - do they all function correctly > > with all of the vector flavours? I don't understand the vector > > extensions well enough to evaluate that - I know that they do check for > > the individual extensions like Zvkb during probe but don't have anything > > for the vector version (at least in the chacha20 and sha256 glue code). > > If they don't, then we need to make sure those drivers do not probe with > > the cut-down variants. > > As far as I know, none of the RISC-V vector crypto code has been tested with > Zve* yet. Currently it always checks for VLEN >= 128, which should exclude most > Zve* implementations. > > Currently it doesn't check for EEW >= 64, even though it sometimes assumes that. > It looks like a check for EEW >= 64 needs to be added in order to exclude Zve32x > and Zve32f implementations that don't support EEW == 64. Cool, glad I asked then :) > If it would be useful to do so, we should be able to enable some of the code > with a smaller VLEN and/or EEW once it has been tested in those configurations. > Some of it should work, but some of it won't be able to work. (For example, the > SHA512 instructions require EEW==64.) > > Also note that currently all the RISC-V vector crypto code only supports riscv64 > (XLEN=64). Similarly, that could be relaxed in the future if people really need > the vector crypto acceleration on 32-bit CPUs... But similarly, the code would > need to be revised and tested in that configuration. > > > Eric/Jerry (although read the previous paragraph too): > > I noticed that the sha256 glue code calls crypto_simd_usable(), and in > > turn may_use_simd() before kernel_vector_begin(). The chacha20 glue code > > does not call either, which seems to violate the edict in > > kernel_vector_begin()'s kerneldoc: > > "Must not be called unless may_use_simd() returns true." > > skcipher algorithms can only be invoked in process and softirq context. This > differs from shash algorithms which can be invoked in any context. > > My understanding is that, like arm64, RISC-V always allows non-nested > kernel-mode vector to be used in process and softirq context -- and in fact, > this was intentionally done in order to support use cases like this. So that's > why the RISC-V skcipher algorithms don't check for may_use_simd() before calling > kernel_vector_begin(). I see, thanks for explaining that. I think you should probably check somewhere if has_vector() returns true in that driver though before using vector instructions. Only checking vlen seems to me like relying on an implementation detail and if we set vlen for the T-Head/0.7.1 vector it'd be fooled. That said, I don't think that any of the 0.7.1 vector systems actually support Zvkb, but I hope you get my drift. Thanks, Conor.
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