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Message-ID: <ZHELoziooIyk0d+t@linux.dev>
Date: Fri, 26 May 2023 19:42:27 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: maz@...nel.org, linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
tabba@...gle.com, qperret@...gle.com, will@...nel.org,
catalin.marinas@....com, yuzenghui@...wei.com,
suzuki.poulose@....com, james.morse@....com, bgardon@...gle.com,
gshan@...hat.com
Subject: Re: [PATCH v2] KVM: arm64: Use BTI for nvhe
Hi Mostafa,
On Wed, May 17, 2023 at 05:35:52PM +0000, Mostafa Saleh wrote:
> CONFIG_ARM64_BTI_KERNEL compiles the kernel to support ARMv8.5-BTI.
> However, the nvhe code doesn't make use of it as it doesn't map any
> pages with Guarded Page(GP) bit.
>
> This patch maps nvhe(and pKVM recreated mapping of) .text section
> with GP bit which matches the kernel handling for BTI.
>
> A new flag is added to enum kvm_pgtable_prot: KVM_PGTABLE_PROT_GP_S1,
> which represents BTI guarded page in hypervisor stage-1 page table.
>
> At hyp init, SCTLR_EL2.BT is set to 1 to match EL1 configuration
> (SCTLR_EL1.BT1) set in bti_enable().
>
> hyp_init_valid_leaf_pte is added to avoid unnecessary considering GP
> bit for stage-2.
>
> Signed-off-by: Mostafa Saleh <smostafa@...gle.com>
> ---
> v1 -> v2:
> - Enable BTI for nvhe also.
> - Only set GP bit for executable pages from pgtable code.
> - Set SCTLR_EL2.BT when BTI is used.
> - use system_supports_bti() for consistency.
> - Add hyp_init_valid_leaf_pte.
> v1: https://lore.kernel.org/all/20230516141846.792193-1-smostafa@google.com/
> ---
> arch/arm64/include/asm/kvm_pgtable.h | 3 +++
> arch/arm64/include/asm/sysreg.h | 1 +
> arch/arm64/kvm/arm.c | 7 ++++++-
> arch/arm64/kvm/hyp/nvhe/hyp-init.S | 7 +++++++
> arch/arm64/kvm/hyp/nvhe/setup.c | 8 ++++++--
> arch/arm64/kvm/hyp/pgtable.c | 11 ++++++++++-
> 6 files changed, 33 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 4cd6762bda80..5bcd06d664d3 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -151,6 +151,7 @@ enum kvm_pgtable_stage2_flags {
> * @KVM_PGTABLE_PROT_W: Write permission.
> * @KVM_PGTABLE_PROT_R: Read permission.
> * @KVM_PGTABLE_PROT_DEVICE: Device attributes.
> + * @KVM_PGTABLE_PROT_GP_S1: GP(guarded page) used for BTI in stage-1 only
> * @KVM_PGTABLE_PROT_SW0: Software bit 0.
> * @KVM_PGTABLE_PROT_SW1: Software bit 1.
> * @KVM_PGTABLE_PROT_SW2: Software bit 2.
> @@ -163,6 +164,8 @@ enum kvm_pgtable_prot {
>
> KVM_PGTABLE_PROT_DEVICE = BIT(3),
>
> + KVM_PGTABLE_PROT_GP_S1 = BIT(50),
> +
This enumeration is used to generically describe permissions that could
be applied to either stage-1 or stage-2.
Can't we just have KVM_PGTABLE_PROT_X imply GP at hyp stage-1, assuming
BTI is available and we're using it for the kernel?
> KVM_PGTABLE_PROT_SW0 = BIT(55),
> KVM_PGTABLE_PROT_SW1 = BIT(56),
> KVM_PGTABLE_PROT_SW2 = BIT(57),
[...]
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 3d61bd3e591d..9f68e4ce6d14 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -152,6 +152,13 @@ static kvm_pte_t kvm_init_valid_leaf_pte(u64 pa, kvm_pte_t attr, u32 level)
> return pte;
> }
>
> +static kvm_pte_t hyp_init_valid_leaf_pte(u64 pa, kvm_pte_t attr, u32 level)
> +{
> + kvm_pte_t pte = kvm_init_valid_leaf_pte(pa, attr, level);
> +
> + return pte | (attr & KVM_PGTABLE_PROT_GP_S1);
This is a bit of a hack to cram the GP bit back in. I'm guessing the
fact that our ATTR_HI mask doesn't include bit 50 led you here.
My interpretation DDI0487J D8.3.2 is that the upper attribute field is
63:50 for both stages of translation, but bit 50 is RES0 for stage-2.
So, rather than going this route, I'd recommend tweaking the ATTR_HI
mask to include bit 50.
> +}
> +
> static kvm_pte_t kvm_init_invalid_leaf_owner(u8 owner_id)
> {
> return FIELD_PREP(KVM_INVALID_PTE_OWNER_MASK, owner_id);
> @@ -371,6 +378,8 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
>
> if (device)
> return -EINVAL;
> +
> + attr |= prot & KVM_PGTABLE_PROT_GP_S1;
With the above suggestions, this would become:
if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && system_supports_bti())
attr |= KVM_PTE_LEAF_ATTR_HI_S1_GP;
> } else {
> attr |= KVM_PTE_LEAF_ATTR_HI_S1_XN;
> }
> @@ -414,7 +423,7 @@ static bool hyp_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
> return false;
>
> data->phys += granule;
> - new = kvm_init_valid_leaf_pte(phys, data->attr, ctx->level);
> + new = hyp_init_valid_leaf_pte(phys, data->attr, ctx->level);
> if (ctx->old == new)
> return true;
> if (!kvm_pte_valid(ctx->old))
> --
> 2.40.1.698.g37aff9b760-goog
>
--
Thanks,
Oliver
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