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Date: Tue, 8 Mar 2022 15:09:18 -0800
From: Kalesh Singh <kaleshsingh@...gle.com>
To: Stephen Boyd <swboyd@...omium.org>
Cc: Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
Quentin Perret <qperret@...gle.com>,
Fuad Tabba <tabba@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
"Cc: Android Kernel" <kernel-team@...roid.com>,
James Morse <james.morse@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>,
Mark Brown <broonie@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Peter Collingbourne <pcc@...gle.com>,
"Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
Andrew Scull <ascull@...gle.com>,
"moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)"
<linux-arm-kernel@...ts.infradead.org>,
kvmarm <kvmarm@...ts.cs.columbia.edu>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/8] KVM: arm64: Introduce hyp_alloc_private_va_range()
On Tue, Mar 8, 2022 at 12:21 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
HI Stephen. Thanks for the review.
> Quoting Kalesh Singh (2022-03-07 10:48:59)
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index bc2aba953299..ccb2847ee2f4 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -457,22 +457,17 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
> > return 0;
> > }
> >
> > -static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> > - unsigned long *haddr,
> > - enum kvm_pgtable_prot prot)
> > +
> > +/**
> > + * hyp_alloc_private_va_range - Allocates a private VA range.
> > + * @size: The size of the VA range to reserve.
> > + *
> > + * The private VA range is allocated below io_map_base and
> > + * aligned based on the order of @size.
>
> Add what it returns?
>
> Return: Start address of allocated VA range or some error value... (I don't
> understand this part).
>
> It may also be a good idea to write out what VA is in the description:
>
> The private virtual address (VA) range is allocated below io_map_base
>
Ack
> > + */
> > +unsigned long hyp_alloc_private_va_range(size_t size)
> > {
> > unsigned long base;
> > - int ret = 0;
> > -
> > - if (!kvm_host_owns_hyp_mappings()) {
> > - base = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
> > - phys_addr, size, prot);
> > - if (IS_ERR_OR_NULL((void *)base))
> > - return PTR_ERR((void *)base);
> > - *haddr = base;
> > -
> > - return 0;
> > - }
> >
> > mutex_lock(&kvm_hyp_pgd_mutex);
> >
> > @@ -484,29 +479,53 @@ static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> > *
> > * The allocated size is always a multiple of PAGE_SIZE.
> > */
> > - size = PAGE_ALIGN(size + offset_in_page(phys_addr));
> > - base = io_map_base - size;
> > + base = io_map_base - PAGE_ALIGN(size);
> > +
> > + /* Align the allocation based on the order of its size */
> > + base = ALIGN_DOWN(base, PAGE_SIZE << get_order(size));
> >
> > /*
> > * Verify that BIT(VA_BITS - 1) hasn't been flipped by
> > * allocating the new area, as it would indicate we've
> > * overflowed the idmap/IO address range.
> > */
> > - if ((base ^ io_map_base) & BIT(VA_BITS - 1))
> > - ret = -ENOMEM;
> > + if (!base || (base ^ io_map_base) & BIT(VA_BITS - 1))
> > + base = (unsigned long)ERR_PTR(-ENOMEM);
>
> It looks odd to use an error pointer casted to unsigned long to return
> from an address allocation function. Why not pass a pointer for base
> like the function was written before and return an int from this
> function with 0 for success and negative error value?Otherwise some
> sort of define should made like DMA_MAPPING_ERROR and that can be used
> to indicate to the caller that the allocation failed, or a simple zero
> may work?
I wanted to keep consistent between the pkvm and traditional nvhe
code. I will refactor both *alloc_private_va_range() functions to take
a pointer and return an int error if that's preferred. There would
still be a case of this kind of cast in
__pkvm_create_private_mapping() which does return an unsigned long
address or ERR_PTR(...). It looks like it was made to return the
address to facilitate use as a hypercall (@Quentin CMIW).
>
> > else
> > io_map_base = base;
> >
> > mutex_unlock(&kvm_hyp_pgd_mutex);
> >
> > - if (ret)
> > - goto out;
> > + return base;
> > +}
> > +
> > +static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> > + unsigned long *haddr,
> > + enum kvm_pgtable_prot prot)
> > +{
> > + unsigned long addr;
> > + int ret = 0;
> > +
> > + if (!kvm_host_owns_hyp_mappings()) {
> > + addr = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
> > + phys_addr, size, prot);
> > + if (IS_ERR((void *)addr))
>
> IS_ERR_VALUE()?
Good idea, will remove the extra cast.
>
> > + return PTR_ERR((void *)addr);
> > + *haddr = addr;
> > +
> > + return 0;
> > + }
> > +
> > + size += offset_in_page(phys_addr);
> > + addr = hyp_alloc_private_va_range(size);
> > + if (IS_ERR((void *)addr))
>
> IS_ERR_VALUE()?
Ack
>
> > + return PTR_ERR((void *)addr);
> >
> > - ret = __create_hyp_mappings(base, size, phys_addr, prot);
> > + ret = __create_hyp_mappings(addr, size, phys_addr, prot);
> > if (ret)
> > goto out;
> >
> > - *haddr = base + offset_in_page(phys_addr);
> > + *haddr = addr + offset_in_page(phys_addr);
> > out:
> > return ret;
>
> Would be simpler to remove the goto, or return early.
>
> if (!ret)
> *haddr = addr + offset_in_page(phys_addr);
>
> return ret;
Agreed, I'll remove the goto in the next version.
Thanks,
Kalesh
>
> > }
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