On Mon, 19 Jul 2021 11:47:28 +0100,
Quentin Perret <qperret@xxxxxxxxxx> wrote:
>
> Much of the stage-2 manipulation logic relies on being able to destroy
> block mappings if e.g. installing a smaller mapping in the range. The
> rationale for this behaviour is that stage-2 mappings can always be
> re-created lazily. However, this gets more complicated when the stage-2
> page-table is used to store metadata about the underlying pages. In such
> a case, destroying a block mapping may lead to losing part of the
> state, and confuse the user of those metadata (such as the hypervisor in
> nVHE protected mode).
>
> To fix this, introduce a callback function in the pgtable struct which
> is called during all map operations to determine whether the mappings
> can us blocks, or should be forced to page-granularity level. This is
nit: use?
> used by the hypervisor when creating the host stage-2 to force
> page-level mappings when using non-default protection attributes.
>
> Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/kvm_pgtable.h | 63 +++++++++++++++++----------
> arch/arm64/kvm/hyp/nvhe/mem_protect.c | 16 +++++--
> arch/arm64/kvm/hyp/pgtable.c | 20 +++++++--
> 3 files changed, 69 insertions(+), 30 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index af62203d2f7a..dd72653314c7 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -75,25 +75,6 @@ enum kvm_pgtable_stage2_flags {
> KVM_PGTABLE_S2_IDMAP = BIT(1),
> };
>
> -/**
> - * struct kvm_pgtable - KVM page-table.
> - * @ia_bits: Maximum input address size, in bits.
> - * @start_level: Level at which the page-table walk starts.
> - * @pgd: Pointer to the first top-level entry of the page-table.
> - * @mm_ops: Memory management callbacks.
> - * @mmu: Stage-2 KVM MMU struct. Unused for stage-1 page-tables.
> - */
> -struct kvm_pgtable {
> - u32 ia_bits;
> - u32 start_level;
> - kvm_pte_t *pgd;
> - struct kvm_pgtable_mm_ops *mm_ops;
> -
> - /* Stage-2 only */
> - struct kvm_s2_mmu *mmu;
> - enum kvm_pgtable_stage2_flags flags;
> -};
> -
> /**
> * enum kvm_pgtable_prot - Page-table permissions and attributes.
> * @KVM_PGTABLE_PROT_X: Execute permission.
> @@ -109,11 +90,41 @@ enum kvm_pgtable_prot {
> KVM_PGTABLE_PROT_DEVICE = BIT(3),
> };
>
> -#define PAGE_HYP (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
> +#define KVM_PGTABLE_PROT_RW (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
> +#define KVM_PGTABLE_PROT_RWX (KVM_PGTABLE_PROT_RW | KVM_PGTABLE_PROT_X)
> +
> +#define PAGE_HYP KVM_PGTABLE_PROT_RW
> #define PAGE_HYP_EXEC (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_X)
> #define PAGE_HYP_RO (KVM_PGTABLE_PROT_R)
> #define PAGE_HYP_DEVICE (PAGE_HYP | KVM_PGTABLE_PROT_DEVICE)
>
> +typedef bool (*kvm_pgtable_want_pte_cb_t)(u64 addr, u64 end,
> + enum kvm_pgtable_prot prot);
> +
> +/**
> + * struct kvm_pgtable - KVM page-table.
> + * @ia_bits: Maximum input address size, in bits.
> + * @start_level: Level at which the page-table walk starts.
> + * @pgd: Pointer to the first top-level entry of the page-table.
> + * @mm_ops: Memory management callbacks.
> + * @mmu: Stage-2 KVM MMU struct. Unused for stage-1 page-tables.
> + * @flags: Stage-2 page-table flags.
> + * @want_pte_cb: Callback function used during map operations to decide
> + * whether block mappings can be used to map the given IPA
> + * range.
> + */
> +struct kvm_pgtable {
> + u32 ia_bits;
> + u32 start_level;
> + kvm_pte_t *pgd;
> + struct kvm_pgtable_mm_ops *mm_ops;
> +
> + /* Stage-2 only */
> + struct kvm_s2_mmu *mmu;
> + enum kvm_pgtable_stage2_flags flags;
> + kvm_pgtable_want_pte_cb_t want_pte_cb;
> +};
nit: does this whole definition really need to move around?
> +
> /**
> * struct kvm_mem_range - Range of Intermediate Physical Addresses
> * @start: Start of the range.
> @@ -216,21 +227,25 @@ int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys,
> u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift);
>
> /**
> - * kvm_pgtable_stage2_init_flags() - Initialise a guest stage-2 page-table.
> + * kvm_pgtable_stage2_init_full() - Initialise a guest stage-2 page-table.
> * @pgt: Uninitialised page-table structure to initialise.
> * @arch: Arch-specific KVM structure representing the guest virtual
> * machine.
> * @mm_ops: Memory management callbacks.
> * @flags: Stage-2 configuration flags.
> + * @want_pte_cb: Callback function used during map operations to decide
> + * whether block mappings can be used to map the given IPA
> + * range.
> *
> * Return: 0 on success, negative error code on failure.
> */
> -int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch,
> +int kvm_pgtable_stage2_init_full(struct kvm_pgtable *pgt, struct kvm_arch *arch,
> struct kvm_pgtable_mm_ops *mm_ops,
> - enum kvm_pgtable_stage2_flags flags);
> + enum kvm_pgtable_stage2_flags flags,
> + kvm_pgtable_want_pte_cb_t want_pte_cb);
>
> #define kvm_pgtable_stage2_init(pgt, arch, mm_ops) \
> - kvm_pgtable_stage2_init_flags(pgt, arch, mm_ops, 0)
> + kvm_pgtable_stage2_init_full(pgt, arch, mm_ops, 0, NULL)
nit: in general, we use __foo() as the primitive for foo(), rather
than foo_with_icing_on_top().
>
> /**
> * kvm_pgtable_stage2_destroy() - Destroy an unused guest stage-2 page-table.
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 58edc62be6f7..cdace80d3e28 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -89,6 +89,7 @@ static void prepare_host_vtcr(void)
> id_aa64mmfr1_el1_sys_val, phys_shift);
> }
>
> +static bool host_stage2_want_pte_cb(u64 addr, u64 end, enum kvm_pgtable_prot prot);
> int kvm_host_prepare_stage2(void *pgt_pool_base)
> {
> struct kvm_s2_mmu *mmu = &host_kvm.arch.mmu;
> @@ -101,8 +102,9 @@ int kvm_host_prepare_stage2(void *pgt_pool_base)
> if (ret)
> return ret;
>
> - ret = kvm_pgtable_stage2_init_flags(&host_kvm.pgt, &host_kvm.arch,
> - &host_kvm.mm_ops, KVM_HOST_S2_FLAGS);
> + ret = kvm_pgtable_stage2_init_full(&host_kvm.pgt, &host_kvm.arch,
> + &host_kvm.mm_ops, KVM_HOST_S2_FLAGS,
> + host_stage2_want_pte_cb);
> if (ret)
> return ret;
>
> @@ -225,9 +227,17 @@ static inline int __host_stage2_idmap(u64 start, u64 end,
> __ret; \
> })
>
> +static bool host_stage2_want_pte_cb(u64 addr, u64 end, enum kvm_pgtable_prot prot)
> +{
> + if (range_is_memory(addr, end))
> + return prot != KVM_PGTABLE_PROT_RWX;
> + else
> + return prot != KVM_PGTABLE_PROT_RW;
> +}
This really deserves a comment about *why* you make such decision. I
also find it a bit odd that you use the permissions to decide whether
to map a block or a not. It feels like the permission is more of a
side effect than anything else.
> +
> static int host_stage2_idmap(u64 addr)
> {
> - enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W;
> + enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_RW;
> struct kvm_mem_range range;
> bool is_memory = find_mem_range(addr, &range);
> int ret;
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 34cf67997a82..5bdbe7a31551 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -452,6 +452,8 @@ int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
> pgt->start_level = KVM_PGTABLE_MAX_LEVELS - levels;
> pgt->mm_ops = mm_ops;
> pgt->mmu = NULL;
> + pgt->want_pte_cb = NULL;
> +
> return 0;
> }
>
> @@ -491,6 +493,7 @@ struct stage2_map_data {
> struct kvm_pgtable_mm_ops *mm_ops;
>
> int ret;
> + bool force_pte;
OK, so you have *two* mechanisms here: once to decide if a range can
be mapped as a block or not, and another one to remember the result
while walking the S2 PTW. This probably deserves some documentation
and/or patch splitting.
> };
>
> u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
> @@ -613,6 +616,9 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
> struct kvm_pgtable *pgt = data->mmu->pgt;
> struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
>
> + if (data->force_pte && (level < (KVM_PGTABLE_MAX_LEVELS - 1)))
> + return -E2BIG;
> +
> if (!kvm_block_mapping_supported(addr, end, phys, level))
> return -E2BIG;
>
> @@ -660,6 +666,9 @@ static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
> if (data->anchor)
> return 0;
>
> + if (data->force_pte && (level < (KVM_PGTABLE_MAX_LEVELS - 1)))
> + return 0;
> +
> if (!kvm_block_mapping_supported(addr, end, data->phys, level))
There is something in me screaming that kvm_block_mapping_supported()
should be the point where we check for these things... Or at least a
helper function that takes 'data' as a parameter.
> return 0;
>
> @@ -791,6 +800,7 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
> .memcache = mc,
> .mm_ops = pgt->mm_ops,
> .ret = 0,
> + .force_pte = pgt->want_pte_cb && pgt->want_pte_cb(addr, addr + size, prot),
Reading this makes me want to rename want_pte_cb() to force_pte_cb()...
> };
> struct kvm_pgtable_walker walker = {
> .cb = stage2_map_walker,
> @@ -826,6 +836,7 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
> .mm_ops = pgt->mm_ops,
> .owner_id = owner_id,
> .ret = 0,
> + .force_pte = true,
> };
> struct kvm_pgtable_walker walker = {
> .cb = stage2_map_walker,
> @@ -1070,9 +1081,11 @@ int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size)
> return kvm_pgtable_walk(pgt, addr, size, &walker);
> }
>
> -int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch,
> - struct kvm_pgtable_mm_ops *mm_ops,
> - enum kvm_pgtable_stage2_flags flags)
> +
> +int kvm_pgtable_stage2_init_full(struct kvm_pgtable *pgt, struct kvm_arch *arch,
> + struct kvm_pgtable_mm_ops *mm_ops,
> + enum kvm_pgtable_stage2_flags flags,
> + kvm_pgtable_want_pte_cb_t want_pte_cb)
> {
> size_t pgd_sz;
> u64 vtcr = arch->vtcr;
> @@ -1090,6 +1103,7 @@ int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch
> pgt->mm_ops = mm_ops;
> pgt->mmu = &arch->mmu;
> pgt->flags = flags;
> + pgt->want_pte_cb = want_pte_cb;
>
> /* Ensure zeroed PGD pages are visible to the hardware walker */
> dsb(ishst);
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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