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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Patrick Roy =0A= =0A= Support for GUEST_MEMFD_FLAG_NO_DIRECT_MAP on arm64 depends on 1) direct=0A= map manipulations at 4k granularity being possible, and 2) FEAT_S2FWB.=0A= =0A= 1) is met whenever the direct map is set up at 4k granularity (e.g. not=0A= with huge/gigantic pages) at boottime, as due to ARM's=0A= break-before-make semantics, breaking huge mappings into 4k mappings in=0A= the direct map is not possible (BBM would require temporary invalidation=0A= of the entire huge mapping, even if only a 4k subrange should be zapped,=0A= which will probably crash the kernel). However, the current default for=0A= rodata_full is true, which forces a 4k direct map.=0A= =0A= 2) is required to allow KVM to elide cache coherency operations when=0A= installing stage 2 page tables, which require the direct map to be=0A= entry for the newly mapped memory to be present (which it will not be,=0A= as guest_memfd would have removed direct map entries in=0A= kvm_gmem_get_pfn()).=0A= =0A= Cc: Will Deacon =0A= Signed-off-by: Patrick Roy =0A= Reviewed-by: David Hildenbrand (Arm) =0A= Signed-off-by: Nikita Kalyazin =0A= ---=0A= arch/arm64/include/asm/kvm_host.h | 13 +++++++++++++=0A= 1 file changed, 13 insertions(+)=0A= =0A= diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm= _host.h=0A= index 70cb9cfd760a..fbdd43e7e94e 100644=0A= --- a/arch/arm64/include/asm/kvm_host.h=0A= +++ b/arch/arm64/include/asm/kvm_host.h=0A= @@ -19,6 +19,7 @@=0A= #include =0A= #include =0A= #include =0A= +#include =0A= #include =0A= #include =0A= #include =0A= @@ -1682,6 +1683,18 @@ static __always_inline enum fgt_group_id __fgt_reg_t= o_group_id(enum vcpu_sysreg=0A= \=0A= p; \=0A= })=0A= +#ifdef CONFIG_KVM_GUEST_MEMFD=0A= +static inline bool kvm_arch_gmem_supports_no_direct_map(struct kvm *kvm)= =0A= +{=0A= + /*=0A= + * Without FWB, direct map access is needed in kvm_pgtable_stage2_map(),= =0A= + * as it calls dcache_clean_inval_poc().=0A= + */=0A= + return can_set_direct_map() && cpus_have_final_cap(ARM64_HAS_STAGE2_FWB);= =0A= +}=0A= +#define kvm_arch_gmem_supports_no_direct_map kvm_arch_gmem_supports_no_dir= ect_map=0A= +#endif /* CONFIG_KVM_GUEST_MEMFD */=0A= +=0A= =0A= long kvm_get_cap_for_kvm_ioctl(unsigned int ioctl, long *ext);=0A= =0A= -- =0A= 2.50.1=0A= =0A=