From: Mark Rutland <mark.rutland@arm.com>
To: Michael Kelley <mikelley@microsoft.com>
Cc: "will@kernel.org" <will@kernel.org>,
"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
"sudeep.holla@arm.com" <sudeep.holla@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
"arnd@arndb.de" <arnd@arndb.de>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
"ardb@kernel.org" <ardb@kernel.org>,
"daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
KY Srinivasan <kys@microsoft.com>
Subject: Re: [PATCH v9 1/7] smccc: Add HVC call variant with result registers other than 0 thru 3
Date: Thu, 25 Mar 2021 09:56:26 +0000 [thread overview]
Message-ID: <20210325095626.GA36570@C02TD0UTHF1T.local> (raw)
In-Reply-To: <MWHPR21MB159351AFC4226A6AA8E33530D7629@MWHPR21MB1593.namprd21.prod.outlook.com>
On Thu, Mar 25, 2021 at 04:55:51AM +0000, Michael Kelley wrote:
> From: Mark Rutland <mark.rutland@arm.com> Sent: Wednesday, March 24, 2021 9:55 AM
> > For the benefit of others here, SMCCCv1.2 allows:
> >
> > * SMC64/HVC64 to use all of x1-x17 for both parameters and return values
> > * SMC32/HVC32 to use all of r1-r7 for both parameters and return values
> >
> > The rationale for this was to make it possible to pass a large number of
> > arguments in one call without the hypervisor/firmware needing to access
> > the memory of the caller.
> >
> > My preference would be to add arm_smccc_1_2_{hvc,smc}() assembly
> > functions which read all the permitted argument registers from a struct,
> > and write all the permitted result registers to a struct, leaving it to
> > callers to set those up and decompose them.
> >
> > That way we only have to write one implementation that all callers can
> > use, which'll be far easier to maintain. I suspect that in general the
> > cost of temporarily bouncing the values through memory will be dominated
> > by whatever the hypervisor/firmware is going to do, and if it's not we
> > can optimize that away in future.
>
> Thanks for the feedback, and I'm working on implementing this approach.
> But I've hit a snag in that gcc limits the "asm" statement to 30 arguments,
> which gives us 15 registers as parameters and 15 registers as return
> values, instead of the 18 each allowed by SMCCC v1.2. I will continue
> with the 15 register limit for now, unless someone knows a way to exceed
> that. The alternative would be to go to pure assembly language.
I realise in retrospect this is not clear, but when I said "assembly
functions" I had meant raw assembly functions rather than inline
assembly.
We already have __arm_smccc_smc and __arm_smccc_hvc assembly functions
in arch/{arm,arm64}/kernel/smccc-call.S, and I'd expected we'd add the
full fat SMCCCv1.2 variants there.
Thanks,
Mark.
next prev parent reply other threads:[~2021-03-25 9:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 19:57 [PATCH v9 0/7] Enable Linux guests on Hyper-V on ARM64 Michael Kelley
2021-03-08 19:57 ` [PATCH v9 1/7] smccc: Add HVC call variant with result registers other than 0 thru 3 Michael Kelley
2021-03-24 16:55 ` Mark Rutland
2021-03-25 4:55 ` Michael Kelley
2021-03-25 9:56 ` Mark Rutland [this message]
2021-03-25 17:19 ` Michael Kelley
2021-03-08 19:57 ` [PATCH v9 2/7] arm64: hyperv: Add Hyper-V hypercall and register access utilities Michael Kelley
2021-03-15 23:02 ` Sunil Muthuswamy
2021-03-08 19:57 ` [PATCH v9 3/7] arm64: hyperv: Add Hyper-V clocksource/clockevent support Michael Kelley
2021-03-08 19:57 ` [PATCH v9 4/7] arm64: hyperv: Add kexec and panic handlers Michael Kelley
2021-03-08 19:57 ` [PATCH v9 5/7] arm64: hyperv: Initialize hypervisor on boot Michael Kelley
2021-03-15 19:54 ` Sunil Muthuswamy
2021-03-08 19:57 ` [PATCH v9 6/7] arm64: efi: Export screen_info Michael Kelley
2021-03-08 19:57 ` [PATCH v9 7/7] Drivers: hv: Enable Hyper-V code to be built on ARM64 Michael Kelley
2021-03-24 15:54 ` [PATCH v9 0/7] Enable Linux guests on Hyper-V " Michael Kelley
2021-04-05 17:45 ` Michael Kelley
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