| Message ID | 20190617185017.32661-2-sstabellini@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4,1/2] xen: switch pdx_init_mask to return uint64_t | expand |
Hi, On 6/17/19 7:50 PM, Stefano Stabellini wrote: > 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> Reviewed-by: Julien Grall <julien.grall@arm.com> Ideally, I would like an ack from Andrew or Jan. > 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 v4: > - use uint64_t > - single line comment code style > > Changes in v3: > - improve in-code comments > > Unchanged in v3: > - (u64)1 > > 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 | 7 ++++++- > 2 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c > index b03e7ac330..b0af90e5bf 100644 > --- a/xen/arch/arm/setup.c > +++ b/xen/arch/arm/setup.c > @@ -483,7 +483,14 @@ static void __init init_pdx(void) > { > paddr_t bank_start, bank_size, bank_end; > > - uint64_t 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. > + */ > + uint64_t 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 8356f03ce8..9990b94f73 100644 > --- a/xen/common/pdx.c > +++ b/xen/common/pdx.c > @@ -50,9 +50,11 @@ static u64 __init fill_mask(u64 mask) > return mask; > } > > +/* We don't compress the first MAX_ORDER bit of the addresses. */ > uint64_t __init pdx_init_mask(uint64_t base_addr) > { > - return fill_mask(base_addr - 1); > + return fill_mask(max(base_addr, > + (uint64_t)1 << (MAX_ORDER + PAGE_SHIFT)) - 1); > } > > u64 __init pdx_region_mask(u64 base, u64 len) > @@ -80,6 +82,9 @@ 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; ; ) > { >
>>> On 20.06.19 at 15:20, <julien.grall@arm.com> wrote: > On 6/17/19 7:50 PM, Stefano Stabellini wrote: >> 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> > > Reviewed-by: Julien Grall <julien.grall@arm.com> > > Ideally, I would like an ack from Andrew or Jan. Acked-by: Jan Beulich <jbeulich@suse.com> with one more minor remark: >> --- a/xen/common/pdx.c >> +++ b/xen/common/pdx.c >> @@ -50,9 +50,11 @@ static u64 __init fill_mask(u64 mask) >> return mask; >> } >> >> +/* We don't compress the first MAX_ORDER bit of the addresses. */ >> uint64_t __init pdx_init_mask(uint64_t base_addr) I think the comment would benefit from "want to" getting inserted. And as a nit, it should be "bits", not "bit", plus perhaps "low" instead of "first". Jan
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c index b03e7ac330..b0af90e5bf 100644 --- a/xen/arch/arm/setup.c +++ b/xen/arch/arm/setup.c @@ -483,7 +483,14 @@ static void __init init_pdx(void) { paddr_t bank_start, bank_size, bank_end; - uint64_t 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. + */ + uint64_t 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 8356f03ce8..9990b94f73 100644 --- a/xen/common/pdx.c +++ b/xen/common/pdx.c @@ -50,9 +50,11 @@ static u64 __init fill_mask(u64 mask) return mask; } +/* We don't compress the first MAX_ORDER bit of the addresses. */ uint64_t __init pdx_init_mask(uint64_t base_addr) { - return fill_mask(base_addr - 1); + return fill_mask(max(base_addr, + (uint64_t)1 << (MAX_ORDER + PAGE_SHIFT)) - 1); } u64 __init pdx_region_mask(u64 base, u64 len) @@ -80,6 +82,9 @@ 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 v4: - use uint64_t - single line comment code style Changes in v3: - improve in-code comments Unchanged in v3: - (u64)1 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 | 7 ++++++- 2 files changed, 14 insertions(+), 2 deletions(-)