^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) =================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) The PPC KVM paravirtual interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) =================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) The basic execution principle by which KVM on PowerPC works is to run all kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) space code in PR=1 which is user space. This way we trap all privileged
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) instructions and can emulate them accordingly.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) Unfortunately that is also the downfall. There are quite some privileged
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) instructions that needlessly return us to the hypervisor even though they
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) could be handled differently.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) This is what the PPC PV interface helps with. It takes privileged instructions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) and transforms them into unprivileged ones with some help from the hypervisor.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) This cuts down virtualization costs by about 50% on some of my benchmarks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) The code for that interface can be found in arch/powerpc/kernel/kvm*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) Querying for existence
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) ======================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) To find out if we're running on KVM or not, we leverage the device tree. When
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) Linux is running on KVM, a node /hypervisor exists. That node contains a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) compatible property with the value "linux,kvm".
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) Once you determined you're running under a PV capable KVM, you can now use
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) hypercalls as described below.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) KVM hypercalls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) ==============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) Inside the device tree's /hypervisor node there's a property called
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) 'hypercall-instructions'. This property contains at most 4 opcodes that make
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) up the hypercall. To call a hypercall, just call these instructions.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) The parameters are as follows:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) ======== ================ ================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) Register IN OUT
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) ======== ================ ================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) r0 - volatile
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) r3 1st parameter Return code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) r4 2nd parameter 1st output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) r5 3rd parameter 2nd output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) r6 4th parameter 3rd output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) r7 5th parameter 4th output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) r8 6th parameter 5th output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) r9 7th parameter 6th output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) r10 8th parameter 7th output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) r11 hypercall number 8th output value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) r12 - volatile
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) ======== ================ ================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) Hypercall definitions are shared in generic code, so the same hypercall numbers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) apply for x86 and powerpc alike with the exception that each KVM hypercall
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) also needs to be ORed with the KVM vendor code which is (42 << 16).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) Return codes can be as follows:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) ==== =========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) Code Meaning
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) ==== =========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) 0 Success
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) 12 Hypercall not implemented
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) <0 Error
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) ==== =========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) The magic page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) ==============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) To enable communication between the hypervisor and guest there is a new shared
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) page that contains parts of supervisor visible register state. The guest can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) map this shared page using the KVM hypercall KVM_HC_PPC_MAP_MAGIC_PAGE.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) With this hypercall issued the guest always gets the magic page mapped at the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) desired location. The first parameter indicates the effective address when the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) MMU is enabled. The second parameter indicates the address in real mode, if
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) applicable to the target. For now, we always map the page to -4096. This way we
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) can access it using absolute load and store functions. The following
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) instruction reads the first field of the magic page::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) ld rX, -4096(0)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) The interface is designed to be extensible should there be need later to add
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) additional registers to the magic page. If you add fields to the magic page,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) also define a new hypercall feature to indicate that the host can give you more
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) registers. Only if the host supports the additional features, make use of them.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) The magic page layout is described by struct kvm_vcpu_arch_shared
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) in arch/powerpc/include/asm/kvm_para.h.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) Magic page features
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) ===================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) When mapping the magic page using the KVM hypercall KVM_HC_PPC_MAP_MAGIC_PAGE,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) a second return value is passed to the guest. This second return value contains
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) a bitmap of available features inside the magic page.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) The following enhancements to the magic page are currently available:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) ============================ =======================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) KVM_MAGIC_FEAT_SR Maps SR registers r/w in the magic page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) KVM_MAGIC_FEAT_MAS0_TO_SPRG7 Maps MASn, ESR, PIR and high SPRGs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) ============================ =======================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) For enhanced features in the magic page, please check for the existence of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) feature before using them!
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) Magic page flags
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) ================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) In addition to features that indicate whether a host is capable of a particular
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) feature we also have a channel for a guest to tell the guest whether it's capable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) of something. This is what we call "flags".
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) Flags are passed to the host in the low 12 bits of the Effective Address.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) The following flags are currently available for a guest to expose:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) MAGIC_PAGE_FLAG_NOT_MAPPED_NX Guest handles NX bits correctly wrt magic page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) MSR bits
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) The MSR contains bits that require hypervisor intervention and bits that do
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) not require direct hypervisor intervention because they only get interpreted
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) when entering the guest or don't have any impact on the hypervisor's behavior.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) The following bits are safe to be set inside the guest:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) - MSR_EE
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) - MSR_RI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) If any other bit changes in the MSR, please still use mtmsr(d).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) Patched instructions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) ====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) The "ld" and "std" instructions are transformed to "lwz" and "stw" instructions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) respectively on 32 bit systems with an added offset of 4 to accommodate for big
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) endianness.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) The following is a list of mapping the Linux kernel performs when running as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) guest. Implementing any of those mappings is optional, as the instruction traps
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) also act on the shared page. So calling privileged instructions still works as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) before.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) ======================= ================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) From To
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) ======================= ================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) mfmsr rX ld rX, magic_page->msr
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) mfsprg rX, 0 ld rX, magic_page->sprg0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) mfsprg rX, 1 ld rX, magic_page->sprg1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156) mfsprg rX, 2 ld rX, magic_page->sprg2
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) mfsprg rX, 3 ld rX, magic_page->sprg3
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) mfsrr0 rX ld rX, magic_page->srr0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) mfsrr1 rX ld rX, magic_page->srr1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) mfdar rX ld rX, magic_page->dar
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) mfdsisr rX lwz rX, magic_page->dsisr
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) mtmsr rX std rX, magic_page->msr
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) mtsprg 0, rX std rX, magic_page->sprg0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) mtsprg 1, rX std rX, magic_page->sprg1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) mtsprg 2, rX std rX, magic_page->sprg2
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) mtsprg 3, rX std rX, magic_page->sprg3
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) mtsrr0 rX std rX, magic_page->srr0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) mtsrr1 rX std rX, magic_page->srr1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) mtdar rX std rX, magic_page->dar
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) mtdsisr rX stw rX, magic_page->dsisr
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) tlbsync nop
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) mtmsrd rX, 0 b <special mtmsr section>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176) mtmsr rX b <special mtmsr section>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) mtmsrd rX, 1 b <special mtmsrd section>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180) [Book3S only]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) mtsrin rX, rY b <special mtsrin section>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) [BookE only]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) wrteei [0|1] b <special wrteei section>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) ======================= ================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) Some instructions require more logic to determine what's going on than a load
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) or store instruction can deliver. To enable patching of those, we keep some
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189) RAM around where we can live translate instructions to. What happens is the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) following:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) 1) copy emulation code to memory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) 2) patch that code to fit the emulated instruction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) 3) patch that code to return to the original pc + 4
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) 4) patch the original instruction to branch to the new code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197) That way we can inject an arbitrary amount of code as replacement for a single
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) instruction. This allows us to check for pending interrupts when setting EE=1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) for example.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) Hypercall ABIs in KVM on PowerPC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) =================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) 1) KVM hypercalls (ePAPR)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) These are ePAPR compliant hypercall implementation (mentioned above). Even
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) generic hypercalls are implemented here, like the ePAPR idle hcall. These are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) available on all targets.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) 2) PAPR hypercalls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) PAPR hypercalls are needed to run server PowerPC PAPR guests (-M pseries in QEMU).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) These are the same hypercalls that pHyp, the POWER hypervisor implements. Some of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214) them are handled in the kernel, some are handled in user space. This is only
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) available on book3s_64.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) 3) OSI hypercalls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) Mac-on-Linux is another user of KVM on PowerPC, which has its own hypercall (long
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) before KVM). This is supported to maintain compatibility. All these hypercalls get
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) forwarded to user space. This is only useful on book3s_32, but can be used with
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) book3s_64 as well.
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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