Re: [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler
On 8/14/19 3:34 PM, Segher Boessenkool wrote: > On Wed, Aug 14, 2019 at 08:46:15PM +1000, Michael Ellerman wrote: >> Claudio Carvalho writes: >>> +_GLOBAL(ucall_norets) >>> +EXPORT_SYMBOL_GPL(ucall_norets) >>> + mfcrr0 >>> + stw r0,8(r1) >>> + >>> + sc 2 /* Invoke the ultravisor */ >>> + >>> + lwz r0,8(r1) >>> + mtcrf 0xff,r0 >>> + blr /* Return r3 = status */ >> Paulus points that we shouldn't need to save CR here. Our caller will >> have already saved it if it needed to, and we don't use CR in this >> function so we don't need to save it. >> >> That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are >> non-volatile (PAPR § 14.5.3). > And assuming the ultravisor already clears (or sets, or whatever) all CR > fields it does not want to leak the contents of (which it also should, > of course). Thanks Segher. We are working on that in the ultravisor source code. Claudio. > >> I know plpar_hcall_norets() does save CR, but it shouldn't need to, that >> seems to be historical. aka. no one knows why it does it but it always >> has. > > Segher >
Re: [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler
On 8/14/19 7:46 AM, Michael Ellerman wrote: > Claudio Carvalho writes: >> diff --git a/arch/powerpc/kernel/ucall.S b/arch/powerpc/kernel/ucall.S >> new file mode 100644 >> index ..de9133e45d21 >> --- /dev/null >> +++ b/arch/powerpc/kernel/ucall.S >> @@ -0,0 +1,20 @@ >> +/* SPDX-License-Identifier: GPL-2.0 */ >> +/* >> + * Generic code to perform an ultravisor call. >> + * >> + * Copyright 2019, IBM Corporation. >> + * >> + */ >> +#include >> +#include >> + >> +_GLOBAL(ucall_norets) >> +EXPORT_SYMBOL_GPL(ucall_norets) >> +mfcrr0 >> +stw r0,8(r1) >> + >> +sc 2 /* Invoke the ultravisor */ >> + >> +lwz r0,8(r1) >> +mtcrf 0xff,r0 >> +blr /* Return r3 = status */ > Paulus points that we shouldn't need to save CR here. Our caller will > have already saved it if it needed to, and we don't use CR in this > function so we don't need to save it. Dropped the CR save/restore in the next patchset version: _GLOBAL(ucall_norets) EXPORT_SYMBOL_GPL(ucall_norets) sc 2 /* Invoke the ultravisor */ blr /* Return r3 = status */ Thanks, Claudio > > That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are > non-volatile (PAPR § 14.5.3). > > I know plpar_hcall_norets() does save CR, but it shouldn't need to, that > seems to be historical. aka. no one knows why it does it but it always > has. > > cheers >
Re: [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler
On Wed, Aug 14, 2019 at 08:46:15PM +1000, Michael Ellerman wrote: > Claudio Carvalho writes: > > +_GLOBAL(ucall_norets) > > +EXPORT_SYMBOL_GPL(ucall_norets) > > + mfcrr0 > > + stw r0,8(r1) > > + > > + sc 2 /* Invoke the ultravisor */ > > + > > + lwz r0,8(r1) > > + mtcrf 0xff,r0 > > + blr /* Return r3 = status */ > > Paulus points that we shouldn't need to save CR here. Our caller will > have already saved it if it needed to, and we don't use CR in this > function so we don't need to save it. > > That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are > non-volatile (PAPR § 14.5.3). And assuming the ultravisor already clears (or sets, or whatever) all CR fields it does not want to leak the contents of (which it also should, of course). > I know plpar_hcall_norets() does save CR, but it shouldn't need to, that > seems to be historical. aka. no one knows why it does it but it always > has. Segher
Re: [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler
Claudio Carvalho writes: > diff --git a/arch/powerpc/kernel/ucall.S b/arch/powerpc/kernel/ucall.S > new file mode 100644 > index ..de9133e45d21 > --- /dev/null > +++ b/arch/powerpc/kernel/ucall.S > @@ -0,0 +1,20 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Generic code to perform an ultravisor call. > + * > + * Copyright 2019, IBM Corporation. > + * > + */ > +#include > +#include > + > +_GLOBAL(ucall_norets) > +EXPORT_SYMBOL_GPL(ucall_norets) > + mfcrr0 > + stw r0,8(r1) > + > + sc 2 /* Invoke the ultravisor */ > + > + lwz r0,8(r1) > + mtcrf 0xff,r0 > + blr /* Return r3 = status */ Paulus points that we shouldn't need to save CR here. Our caller will have already saved it if it needed to, and we don't use CR in this function so we don't need to save it. That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are non-volatile (PAPR § 14.5.3). I know plpar_hcall_norets() does save CR, but it shouldn't need to, that seems to be historical. aka. no one knows why it does it but it always has. cheers
