| Message ID | 20190603220245.22750-3-sstabellini@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3,1/3] xen/arm: fix nr_pdxs calculation | expand |
Hi, On 6/3/19 11:02 PM, Stefano Stabellini wrote: > diff --git a/xen/common/pdx.c b/xen/common/pdx.c > index bb7e437049..a3c6f4c1ee 100644 > --- a/xen/common/pdx.c > +++ b/xen/common/pdx.c > @@ -50,9 +50,12 @@ static u64 __init fill_mask(u64 mask) > return mask; > } > > +/* > + * We don't compress the first MAX_ORDER bit of the addresses. > + */ > u64 __init pdx_init_mask(u64 base_addr) > { > - return fill_mask(base_addr - 1); > + return fill_mask(max(base_addr, (u64)1 << (MAX_ORDER + PAGE_SHIFT)) - 1); See my comment on v2 regarding u64 vs uint64_t. Cheers,
>>> On 04.06.19 at 00:02, <sstabellini@kernel.org> wrote: > --- a/xen/arch/arm/setup.c > +++ b/xen/arch/arm/setup.c > @@ -482,7 +482,14 @@ static void __init init_pdx(void) > { > paddr_t bank_start, bank_size, bank_end; > > - u64 mask = pdx_init_mask(bootinfo.mem.bank[0].start); > + /* > + * Arm does not have any restrictions on the bits to compress. Pass 0 to > + * let the common code further restrict the mask. > + * > + * If the logic changes in pfn_pdx_hole_setup we might have to > + * update this function too. > + */ > + u64 mask = pdx_init_mask(0x0); Seeing Julien's clarification on the previous version's discussion, how about switching this one to uint64_t as well at this occasion? > --- a/xen/common/pdx.c > +++ b/xen/common/pdx.c > @@ -50,9 +50,12 @@ static u64 __init fill_mask(u64 mask) > return mask; > } > > +/* > + * We don't compress the first MAX_ORDER bit of the addresses. > + */ This is a single line comment. > u64 __init pdx_init_mask(u64 base_addr) It wouldn't hamper patch readability much if even this one was switched to uint64_t at the same time, thus restoring consistency with ... > { > - return fill_mask(base_addr - 1); > + return fill_mask(max(base_addr, (u64)1 << (MAX_ORDER + PAGE_SHIFT)) - 1); ... the requested use of uint64_t here. Jan
Hi Jan, On 6/4/19 7:56 AM, Jan Beulich wrote: >>>> On 04.06.19 at 00:02, <sstabellini@kernel.org> wrote: >> --- a/xen/arch/arm/setup.c >> +++ b/xen/arch/arm/setup.c >> @@ -482,7 +482,14 @@ static void __init init_pdx(void) >> { >> paddr_t bank_start, bank_size, bank_end; >> >> - u64 mask = pdx_init_mask(bootinfo.mem.bank[0].start); >> + /* >> + * Arm does not have any restrictions on the bits to compress. Pass 0 to >> + * let the common code further restrict the mask. >> + * >> + * If the logic changes in pfn_pdx_hole_setup we might have to >> + * update this function too. >> + */ >> + u64 mask = pdx_init_mask(0x0); > > Seeing Julien's clarification on the previous version's discussion, > how about switching this one to uint64_t as well at this occasion? > >> --- a/xen/common/pdx.c >> +++ b/xen/common/pdx.c >> @@ -50,9 +50,12 @@ static u64 __init fill_mask(u64 mask) >> return mask; >> } >> >> +/* >> + * We don't compress the first MAX_ORDER bit of the addresses. >> + */ > > This is a single line comment. > >> u64 __init pdx_init_mask(u64 base_addr) > > It wouldn't hamper patch readability much if even this one was > switched to uint64_t at the same time, thus restoring consistency > with ... On Arm we don't tend to mix clean-up and fix. It would be preferable if the switch to uint64_t is done in a separate patch. Cheers,
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c index ccb0f181ea..45312df006 100644 --- a/xen/arch/arm/setup.c +++ b/xen/arch/arm/setup.c @@ -482,7 +482,14 @@ static void __init init_pdx(void) { paddr_t bank_start, bank_size, bank_end; - u64 mask = pdx_init_mask(bootinfo.mem.bank[0].start); + /* + * Arm does not have any restrictions on the bits to compress. Pass 0 to + * let the common code further restrict the mask. + * + * If the logic changes in pfn_pdx_hole_setup we might have to + * update this function too. + */ + u64 mask = pdx_init_mask(0x0); int bank; for ( bank = 0 ; bank < bootinfo.mem.nr_banks; bank++ ) diff --git a/xen/common/pdx.c b/xen/common/pdx.c index bb7e437049..a3c6f4c1ee 100644 --- a/xen/common/pdx.c +++ b/xen/common/pdx.c @@ -50,9 +50,12 @@ static u64 __init fill_mask(u64 mask) return mask; } +/* + * We don't compress the first MAX_ORDER bit of the addresses. + */ u64 __init pdx_init_mask(u64 base_addr) { - return fill_mask(base_addr - 1); + return fill_mask(max(base_addr, (u64)1 << (MAX_ORDER + PAGE_SHIFT)) - 1); } u64 __init pdx_region_mask(u64 base, u64 len) @@ -80,6 +83,9 @@ void __init pfn_pdx_hole_setup(unsigned long mask) * This guarantees that page-pointer arithmetic remains valid within * contiguous aligned ranges of 2^MAX_ORDER pages. Among others, our * buddy allocator relies on this assumption. + * + * If the logic changes here, we might have to update the ARM specific + * init_pdx too. */ for ( j = MAX_ORDER-1; ; ) {
The mask calculation in pdx_init_mask is wrong when the first bank starts at address 0x0. The reason is that pdx_init_mask will do '0 - 1' causing an underflow. As a result, the mask becomes 0xffffffffffffffff which is the biggest possible mask and ends up causing a significant memory waste in the frametable size computation. For instance, on platforms that have a low memory bank starting at 0x0 and a high memory bank, the frametable will end up covering all the holes in between. The purpose of the mask is to be passed as a parameter to pfn_pdx_hole_setup, which based on the mask parameter calculates pfn_pdx_hole_shift, pfn_pdx_bottom_mask, etc. which are actually the important masks for frametable initialization later on. pfn_pdx_hole_setup never compresses addresses below MAX_ORDER bits (1GB on ARM). Thus, it is safe to initialize mask passing 1ULL << (MAX_ORDER + PAGE_SHIFT) as start address to pdx_init_mask. Signed-off-by: Stefano Stabellini <stefanos@xilinx.com> CC: JBeulich@suse.com CC: andrew.cooper3@citrix.com CC: George.Dunlap@eu.citrix.com CC: ian.jackson@eu.citrix.com CC: konrad.wilk@oracle.com CC: tim@xen.org CC: wei.liu2@citrix.com --- Changes in v3: - improve in-code comments Changes in v2: - update commit message - add in-code comments regarding update sites - improve in-code comments - move the mask initialization changes to pdx_init_mask --- xen/arch/arm/setup.c | 9 ++++++++- xen/common/pdx.c | 8 +++++++- 2 files changed, 15 insertions(+), 2 deletions(-)