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Message-ID: <CAC_TJvfK3zJ_dN-0E3xJOWjdDybU12UfocoMf6-ji_swExas_Q@mail.gmail.com>
Date: Mon, 18 Apr 2022 19:25:58 -0700
From: Kalesh Singh <kaleshsingh@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: Will Deacon <will@...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>,
Andrew Jones <drjones@...hat.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Masahiro Yamada <masahiroy@...nel.org>,
Changbin Du <changbin.du@...el.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 v7 3/6] KVM: arm64: Add guard pages for KVM nVHE
hypervisor stack
On Mon, Apr 18, 2022 at 3:01 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Fri, 08 Apr 2022 21:03:26 +0100,
> Kalesh Singh <kaleshsingh@...gle.com> wrote:
> >
> > Map the stack pages in the flexible private VA range and allocate
> > guard pages below the stack as unbacked VA space. The stack is aligned
> > so that any valid stack address has PAGE_SHIFT bit as 1 - this is used
> > for overflow detection (implemented in a subsequent patch in the series).
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> > Tested-by: Fuad Tabba <tabba@...gle.com>
> > Reviewed-by: Fuad Tabba <tabba@...gle.com>
> > ---
> >
> > Changes in v7:
> > - Add Fuad's Reviewed-by and Tested-by tags.
> >
> > Changes in v6:
> > - Update call to hyp_alloc_private_va_range() (return val and params)
> >
> > Changes in v5:
> > - Use a single allocation for stack and guard pages to ensure they
> > are contiguous, per Marc
> >
> > Changes in v4:
> > - Replace IS_ERR_OR_NULL check with IS_ERR check now that
> > hyp_alloc_private_va_range() returns an error for null
> > pointer, per Fuad
> > - Format comments to < 80 cols, per Fuad
> >
> > Changes in v3:
> > - Handle null ptr in IS_ERR_OR_NULL checks, per Mark
> >
> >
> > arch/arm64/include/asm/kvm_asm.h | 1 +
> > arch/arm64/include/asm/kvm_mmu.h | 3 +++
> > arch/arm64/kvm/arm.c | 39 +++++++++++++++++++++++++++++---
> > arch/arm64/kvm/mmu.c | 4 ++--
> > 4 files changed, 42 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > index d5b0386ef765..2e277f2ed671 100644
> > --- a/arch/arm64/include/asm/kvm_asm.h
> > +++ b/arch/arm64/include/asm/kvm_asm.h
> > @@ -169,6 +169,7 @@ struct kvm_nvhe_init_params {
> > unsigned long tcr_el2;
> > unsigned long tpidr_el2;
> > unsigned long stack_hyp_va;
> > + unsigned long stack_pa;
> > phys_addr_t pgd_pa;
> > unsigned long hcr_el2;
> > unsigned long vttbr;
> > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> > index a50cbb5ba402..b805316c4866 100644
> > --- a/arch/arm64/include/asm/kvm_mmu.h
> > +++ b/arch/arm64/include/asm/kvm_mmu.h
> > @@ -117,6 +117,9 @@ alternative_cb_end
> > #include <asm/mmu_context.h>
> > #include <asm/kvm_host.h>
> >
> > +extern struct kvm_pgtable *hyp_pgtable;
> > +extern struct mutex kvm_hyp_pgd_mutex;
>
> I'd rather you don't expose this at all.
>
> > +
> > void kvm_update_va_mask(struct alt_instr *alt,
> > __le32 *origptr, __le32 *updptr, int nr_inst);
> > void kvm_compute_layout(void);
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 523bc934fe2f..5687c0175151 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -1483,7 +1483,6 @@ static void cpu_prepare_hyp_mode(int cpu)
> > tcr |= (idmap_t0sz & GENMASK(TCR_TxSZ_WIDTH - 1, 0)) << TCR_T0SZ_OFFSET;
> > params->tcr_el2 = tcr;
> >
> > - params->stack_hyp_va = kern_hyp_va(per_cpu(kvm_arm_hyp_stack_page, cpu) + PAGE_SIZE);
> > params->pgd_pa = kvm_mmu_get_httbr();
> > if (is_protected_kvm_enabled())
> > params->hcr_el2 = HCR_HOST_NVHE_PROTECTED_FLAGS;
> > @@ -1933,14 +1932,48 @@ static int init_hyp_mode(void)
> > * Map the Hyp stack pages
> > */
> > for_each_possible_cpu(cpu) {
> > + struct kvm_nvhe_init_params *params = per_cpu_ptr_nvhe_sym(kvm_init_params, cpu);
> > char *stack_page = (char *)per_cpu(kvm_arm_hyp_stack_page, cpu);
> > - err = create_hyp_mappings(stack_page, stack_page + PAGE_SIZE,
> > - PAGE_HYP);
> > + unsigned long hyp_addr;
> >
> > + /*
> > + * Allocate a contiguous HYP private VA range for the stack
> > + * and guard page. The allocation is also aligned based on
> > + * the order of its size.
> > + */
> > + err = hyp_alloc_private_va_range(PAGE_SIZE * 2, &hyp_addr);
> > + if (err) {
> > + kvm_err("Cannot allocate hyp stack guard page\n");
> > + goto out_err;
> > + }
> > +
> > + /*
> > + * Since the stack grows downwards, map the stack to the page
> > + * at the higher address and leave the lower guard page
> > + * unbacked.
> > + *
> > + * Any valid stack address now has the PAGE_SHIFT bit as 1
> > + * and addresses corresponding to the guard page have the
> > + * PAGE_SHIFT bit as 0 - this is used for overflow detection.
> > + */
> > + mutex_lock(&kvm_hyp_pgd_mutex);
> > + err = kvm_pgtable_hyp_map(hyp_pgtable, hyp_addr + PAGE_SIZE,
> > + PAGE_SIZE, __pa(stack_page), PAGE_HYP);
> > + mutex_unlock(&kvm_hyp_pgd_mutex);
>
> The mutex (and the HYP page table structure) really should stay
> private to the MMU code. Just add a new helper that will take the lock
> and use hyp_pgtable.
Agreed. I think we can expose __create_hyp_mappings() instead here.
Thanks,
Kalesh
>
> > if (err) {
> > kvm_err("Cannot map hyp stack\n");
> > goto out_err;
> > }
> > +
> > + /*
> > + * Save the stack PA in nvhe_init_params. This will be needed
> > + * to recreate the stack mapping in protected nVHE mode.
> > + * __hyp_pa() won't do the right thing there, since the stack
> > + * has been mapped in the flexible private VA space.
> > + */
> > + params->stack_pa = __pa(stack_page);
> > +
> > + params->stack_hyp_va = hyp_addr + (2 * PAGE_SIZE);
> > }
> >
> > for_each_possible_cpu(cpu) {
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 3d3efea4e991..a54f00bd06cc 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -22,8 +22,8 @@
> >
> > #include "trace.h"
> >
> > -static struct kvm_pgtable *hyp_pgtable;
> > -static DEFINE_MUTEX(kvm_hyp_pgd_mutex);
> > +struct kvm_pgtable *hyp_pgtable;
> > +DEFINE_MUTEX(kvm_hyp_pgd_mutex);
> >
> > static unsigned long hyp_idmap_start;
> > static unsigned long hyp_idmap_end;
>
> Thanks,
>
> M.
>
> --
> Without deviation from the norm, progress is not possible.
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