Hi Suzuki, On 07/03/2018 01:54 PM, Suzuki K Poulose wrote: > Hi Eric, > > On 02/07/18 15:41, Auger Eric wrote: >> Hi Suzuki, >> >> On 06/29/2018 01:15 PM, Suzuki K Poulose wrote: >>> On arm64 VTTBR_EL2:BADDR holds the base address for the stage2 >>> translation table. The Arm ARM mandates that the bits BADDR[x-1:0] >>> should be 0, where 'x' is defined for a given IPA Size and the >>> number of levels for a translation granule size. It is defined >>> using some magical constants. This patch is a reverse engineered >>> implementation to calculate the 'x' at runtime for a given ipa and >>> number of page table levels. See patch for more details. >>> >>> Cc: Marc Zyngier <marc.zyngier@xxxxxxx> >>> Cc: Christoffer Dall <cdall@xxxxxxxxxx> >>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> >>> --- >>> Changes since V2: >>> - Part 1 of spilt from VTCR & VTTBR dynamic configuration >>> --- >>> arch/arm64/include/asm/kvm_arm.h | 60 >>> +++++++++++++++++++++++++++++++++++++--- >>> arch/arm64/include/asm/kvm_mmu.h | 25 ++++++++++++++++- >>> 2 files changed, 80 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/arm64/include/asm/kvm_arm.h >>> b/arch/arm64/include/asm/kvm_arm.h >>> index 3dffd38..c557f45 100644 >>> --- a/arch/arm64/include/asm/kvm_arm.h >>> +++ b/arch/arm64/include/asm/kvm_arm.h >>> @@ -140,8 +140,6 @@ >>> * Note that when using 4K pages, we concatenate two first level >>> page tables >>> * together. With 16K pages, we concatenate 16 first level page >>> tables. >>> * >>> - * The magic numbers used for VTTBR_X in this patch can be found in >>> Tables >>> - * D4-23 and D4-25 in ARM DDI 0487A.b. >> Isn't it a pretty old reference? Could you refer to C.a? > > Sure, I will update the references everywhere. > >>> + * >>> + * The algorithm defines the expectations on the BaseAddress (for >>> the page >>> + * table) bits resolved at each level based on the page size, entry >>> level >>> + * and T0SZ. The variable "x" in the algorithm also affects the >>> VTTBR:BADDR >>> + * for stage2 page table. >>> + * >>> + * The value of "x" is calculated as : >>> + * x = Magic_N - T0SZ >>> + * >>> + * where Magic_N is an integer depending on the page size and the entry >>> + * level of the page table as below: >>> + * >>> + * -------------------------------------------- >>> + * | Entry level | 4K 16K 64K | >>> + * -------------------------------------------- >>> + * | Level: 0 (4 levels) | 28 | - | - | >>> + * -------------------------------------------- >>> + * | Level: 1 (3 levels) | 37 | 31 | 25 | >>> + * -------------------------------------------- >>> + * | Level: 2 (2 levels) | 46 | 42 | 38 | >>> + * -------------------------------------------- >>> + * | Level: 3 (1 level) | - | 53 | 51 | >>> + * -------------------------------------------- >> I understand entry level = Lookup level in the table. > > Entry level => The level at which we start the page table walk for > a given address (This is in line with the ARM ARM). So, > > Entry_level = (4 - Number_of_Page_table_levels) > >> But you may want to compute x for BaseAddress matching lookup level 2 >> with number of levels = 4. > > No, the BaseAddress is only calcualted for the "Entry_level". So the > above case doesn't exist at all. > >> So shouldn't you s/Number of levels/4 - entry_level? > > Ok, I now understood what you are referring to [0] >> for BADDR we want the BaseAddr of the initial lookup level so >> effectively the entry level we are interested in is 4 - number of levels >> and we don't care or d) condition. At least this is my understanding ;-) >> If correct you may slightly reword the explanation? > > >>> + * >>> + * We have a magic formula for the Magic_N below. >>> + * >>> + * Magic_N(PAGE_SIZE, Entry_Level) = 64 - ((PAGE_SHIFT - 3) * >>> Number of levels) > > [0] ^^^ > > > >>> + * >>> + * where number of levels = (4 - Entry_Level). > > ^^^ Doesn't this help make it clear ? Using the expansion makes it a bit > more > unreadable below. I just wanted to mention the tables you refer (D4-23 and D4-25) give Magic_N for a larger scope as they deal with any lookup level while we only care about the entry level for BADDR. So I was a little bit confused when reading the explanation but that's not a big deal. > >>> +/* >>> + * Get the magic number 'x' for VTTBR:BADDR of this KVM instance. >>> + * With v8.2 LVA extensions, 'x' should be a minimum of 6 with >>> + * 52bit IPS. >> Link to the spec? > > Sure, will add it. > > Thanks for the patience to review :-) you're welcome ;-) Eric > > Cheers > Suzuki
