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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 4/4] x86/hyperv: L0 assisted TLB flush
On Wed, Feb 12, 2020 at 06:43:47PM +0100, Roger Pau Monné wrote:
> On Wed, Feb 12, 2020 at 04:09:18PM +0000, Wei Liu wrote:
> > Implement L0 assisted TLB flush for Xen on Hyper-V. It takes advantage
> > of several hypercalls:
> >
> > * HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST
> > * HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX
> > * HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE
> > * HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX
> >
> > Pick the most efficient hypercalls available.
> >
> > Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> > ---
> > xen/arch/x86/guest/hyperv/Makefile | 1 +
> > xen/arch/x86/guest/hyperv/private.h | 9 ++
> > xen/arch/x86/guest/hyperv/tlb.c | 172 +++++++++++++++++++++++++++-
> > xen/arch/x86/guest/hyperv/util.c | 72 ++++++++++++
> > 4 files changed, 253 insertions(+), 1 deletion(-)
> > create mode 100644 xen/arch/x86/guest/hyperv/util.c
> >
> > diff --git a/xen/arch/x86/guest/hyperv/Makefile
> > b/xen/arch/x86/guest/hyperv/Makefile
> > index 18902c33e9..0e39410968 100644
> > --- a/xen/arch/x86/guest/hyperv/Makefile
> > +++ b/xen/arch/x86/guest/hyperv/Makefile
> > @@ -1,2 +1,3 @@
> > obj-y += hyperv.o
> > obj-y += tlb.o
> > +obj-y += util.o
> > diff --git a/xen/arch/x86/guest/hyperv/private.h
> > b/xen/arch/x86/guest/hyperv/private.h
> > index 78e52f74ce..311f060495 100644
> > --- a/xen/arch/x86/guest/hyperv/private.h
> > +++ b/xen/arch/x86/guest/hyperv/private.h
> > @@ -24,12 +24,21 @@
> >
> > #include <xen/cpumask.h>
> > #include <xen/percpu.h>
> > +#include <xen/types.h>
> >
> > DECLARE_PER_CPU(void *, hv_input_page);
> > DECLARE_PER_CPU(void *, hv_vp_assist);
> > DECLARE_PER_CPU(uint32_t, hv_vp_index);
> >
> > +static inline uint32_t hv_vp_index(int cpu)
>
> unsigned int for cpu.
>
> > +{
> > + return per_cpu(hv_vp_index, cpu);
> > +}
> > +
> > int hyperv_flush_tlb(const cpumask_t *mask, const void *va,
> > unsigned int flags);
> >
> > +/* Returns number of banks, -ev if error */
> > +int cpumask_to_vpset(struct hv_vpset *vpset, const cpumask_t *mask);
> > +
> > #endif /* __XEN_HYPERV_PRIVIATE_H__ */
> > diff --git a/xen/arch/x86/guest/hyperv/tlb.c
> > b/xen/arch/x86/guest/hyperv/tlb.c
> > index 48f527229e..99b789d9e9 100644
> > --- a/xen/arch/x86/guest/hyperv/tlb.c
> > +++ b/xen/arch/x86/guest/hyperv/tlb.c
> > @@ -19,15 +19,185 @@
> > * Copyright (c) 2020 Microsoft.
> > */
> >
> > +#include <xen/cpu.h>
> > #include <xen/cpumask.h>
> > #include <xen/errno.h>
> >
> > +#include <asm/guest/hyperv.h>
> > +#include <asm/guest/hyperv-hcall.h>
> > +#include <asm/guest/hyperv-tlfs.h>
> > +
> > #include "private.h"
> >
> > +/*
> > + * It is possible to encode up to 4096 pages using the lower 12 bits
> > + * in an element of gva_list
> > + */
> > +#define HV_TLB_FLUSH_UNIT (4096 * PAGE_SIZE)
> > +#define ORDER_TO_BYTES(order) ((1ul << (order)) * PAGE_SIZE)
>
> There are already some conversion functions in xen/mm.h
> (get_order_from_{bytes/pages}), maybe you could add a
> get_bytes_from_order helper there?
>
> > +
> > +static unsigned int fill_gva_list(uint64_t *gva_list, const void *va,
> > + unsigned int order)
> > +{
> > + unsigned long start = (unsigned long)va;
> > + unsigned long end = start + ORDER_TO_BYTES(order) - 1;
> > + unsigned int n = 0;
> > +
> > + do {
> > + unsigned long remain = end > start ? end - start : 0;
>
> I don't think you can get here with end == start?
>
> As that's the condition of the loop, and order 0 is going to set
> end = start + 4096 - 1.
Correct. This can be simplified as remain = end - start .
>
> > +
> > + gva_list[n] = start & PAGE_MASK;
> > +
> > + /*
> > + * Use lower 12 bits to encode the number of additional pages
> > + * to flush
> > + */
> > + if ( remain >= HV_TLB_FLUSH_UNIT )
> > + {
> > + gva_list[n] |= ~PAGE_MASK;
> > + start += HV_TLB_FLUSH_UNIT;
> > + }
> > + else if ( remain )
> > + {
> > + gva_list[n] |= (remain - 1) >> PAGE_SHIFT;
> > + start = end;
> > + }
> > +
> > + n++;
> > + } while ( start < end );
> > +
> > + return n;
> > +}
> > +
> > +static uint64_t flush_tlb_ex(const cpumask_t *mask, const void *va,
> > + unsigned int flags)
> > +{
> > + struct hv_tlb_flush_ex *flush = this_cpu(hv_input_page);
> > + int nr_banks;
> > + unsigned int max_gvas;
> > + unsigned int order = flags & FLUSH_ORDER_MASK;
> > + uint64_t ret;
> > +
> > + ASSERT(flush);
> > + ASSERT(!local_irq_is_enabled());
>
> Can you turn this into an if condition with ASSERT_UNREACHABLE and
> return ~0ULL? (as I think that signals an error).
>
There is no need for that. This function will always be internal to
Hyper-V in the foreseeable future. If it is ever called with IRQ enabled
something is wrong with the code.
> > +
> > + if ( !(ms_hyperv.hints & HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED) )
> > + return ~0ULL;
> > +
> > + flush->address_space = 0;
> > + flush->flags = HV_FLUSH_ALL_VIRTUAL_ADDRESS_SPACES;
> > + if ( !(flags & FLUSH_TLB_GLOBAL) )
> > + flush->flags |= HV_FLUSH_NON_GLOBAL_MAPPINGS_ONLY;
> > +
> > + flush->hv_vp_set.valid_bank_mask = 0;
> > + flush->hv_vp_set.format = HV_GENERIC_SET_SPARSE_4K;
> > +
> > + nr_banks = cpumask_to_vpset(&flush->hv_vp_set, mask);
> > + if ( nr_banks < 0 )
> > + return ~0ULL;
> > +
> > + max_gvas =
> > + (PAGE_SIZE - sizeof(*flush) - nr_banks *
> > + sizeof(flush->hv_vp_set.bank_contents[0])) /
> > + sizeof(uint64_t); /* gva is represented as uint64_t */
> > +
> > + /*
> > + * Flush the entire address space if va is NULL or if there is not
> > + * enough space for gva_list.
> > + */
> > + if ( !va || (ORDER_TO_BYTES(order) / HV_TLB_FLUSH_UNIT) > max_gvas )
> > + ret = hv_do_rep_hypercall(HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX, 0,
> > + nr_banks, virt_to_maddr(flush), 0);
> > + else
> > + {
> > + uint64_t *gva_list = (uint64_t *)flush + sizeof(*flush) + nr_banks;
>
> Don't you need nr_banks * sizeof(flush->hv_vp_set.bank_contents) in
> order to calculate the position of the gva_list?
>
The pointer arithmetic is done on uint64_t pointers so it already takes
into account sizeof(bank_contents[0]).
> > + unsigned int gvas = fill_gva_list(gva_list, va, order);
> > +
> > + ret = hv_do_rep_hypercall(HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX,
> > + gvas, nr_banks, virt_to_maddr(flush), 0);
> > + }
> > +
> > + return ret;
> > +}
> > +
> > int hyperv_flush_tlb(const cpumask_t *mask, const void *va,
> > unsigned int flags)
> > {
> > - return -EOPNOTSUPP;
> > + unsigned long irq_flags;
> > + struct hv_tlb_flush *flush = this_cpu(hv_input_page);
> > + uint64_t ret;
> > + unsigned int order = flags & FLUSH_ORDER_MASK;
> > + unsigned int max_gvas;
> > +
> > + ASSERT(flush);
> > + ASSERT(!cpumask_empty(mask));
> > +
> > + local_irq_save(irq_flags);
> > +
> > + flush->address_space = 0;
> > + flush->flags = HV_FLUSH_ALL_VIRTUAL_ADDRESS_SPACES;
> > + flush->processor_mask = 0;
> > + if ( !(flags & FLUSH_TLB_GLOBAL) )
> > + flush->flags |= HV_FLUSH_NON_GLOBAL_MAPPINGS_ONLY;
> > +
> > + if ( cpumask_equal(mask, &cpu_online_map) )
> > + flush->flags |= HV_FLUSH_ALL_PROCESSORS;
> > + else
> > + {
> > + int cpu;
>
> unsigned int.
>
I picked int here and above because all the cpumask functions return
int. I don't mind changing it to unsigned int -- it makes no practical
difference.
> > +
> > + /*
> > + * Normally VP indices are in ascending order and match Xen's
> > + * idea of CPU ids. Check the last index to see if VP index is
> > + * >= 64. If so, we can skip setting up parameters for
> > + * non-applicable hypercalls without looking further.
> > + */
> > + if ( hv_vp_index(cpumask_last(mask)) >= 64 )
> > + goto do_ex_hypercall;
> > +
> > + for_each_cpu ( cpu, mask )
> > + {
> > + uint32_t vpid = hv_vp_index(cpu);
> > +
> > + if ( vpid > ms_hyperv.max_vp_index )
> > + {
> > + local_irq_restore(irq_flags);
> > + return -ENXIO;
> > + }
> > +
> > + if ( vpid >= 64 )
> > + goto do_ex_hypercall;
> > +
> > + __set_bit(vpid, &flush->processor_mask);
> > + }
> > + }
> > +
> > + max_gvas = (PAGE_SIZE - sizeof(*flush)) / sizeof(flush->gva_list[0]);
> > +
> > + /*
> > + * Flush the entire address space if va is NULL or if there is not
> > + * enough space for gva_list.
> > + */
> > + if ( !va || (ORDER_TO_BYTES(order) / HV_TLB_FLUSH_UNIT) > max_gvas )
> > + ret = hv_do_hypercall(HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE,
> > + virt_to_maddr(flush), 0);
> > + else
> > + {
> > + unsigned int gvas = fill_gva_list(flush->gva_list, va, order);
> > +
> > + ret = hv_do_rep_hypercall(HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST, gvas,
> > 0,
> > + virt_to_maddr(flush), 0);
> > + }
> > +
> > + goto done;
> > +
> > + do_ex_hypercall:
> > + ret = flush_tlb_ex(mask, va, flags);
> > +
> > + done:
> > + local_irq_restore(irq_flags);
> > +
> > + return ret & HV_HYPERCALL_RESULT_MASK;
>
> Will this return an error code that uses the same space as Xen's errno
> values?
>
No, it won't. It returns Hyper-V's status code (0 still means success).
I didn't think that was a big deal because non-zero values meant errors.
And the upper layer didn't care about the exact error values (yet).
> > }
> >
> > /*
> > diff --git a/xen/arch/x86/guest/hyperv/util.c
> > b/xen/arch/x86/guest/hyperv/util.c
> > new file mode 100644
> > index 0000000000..9d0b5f4a46
> > --- /dev/null
> > +++ b/xen/arch/x86/guest/hyperv/util.c
> > @@ -0,0 +1,72 @@
> > +/******************************************************************************
> > + * arch/x86/guest/hyperv/util.c
> > + *
> > + * Hyper-V utility functions
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your option) any later version.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program; If not, see <http://www.gnu.org/licenses/>.
> > + *
> > + * Copyright (c) 2020 Microsoft.
> > + */
> > +
> > +#include <xen/cpu.h>
> > +#include <xen/cpumask.h>
> > +#include <xen/errno.h>
> > +
> > +#include <asm/guest/hyperv.h>
> > +#include <asm/guest/hyperv-tlfs.h>
> > +
> > +#include "private.h"
> > +
> > +int cpumask_to_vpset(struct hv_vpset *vpset,
> > + const cpumask_t *mask)
> > +{
> > + int nr = 1, cpu, vcpu_bank, vcpu_offset;
> > + int max_banks = ms_hyperv.max_vp_index / 64;
>
> I think nr whats to be int (to match the function return type), but
> the rest should be unsigned ints, specially because they are used as
> array indexes.
>
OK.
> > +
> > + /* Up to 64 banks can be represented by valid_bank_mask */
> > + if ( max_banks >= 64 )
> > + return -1;
>
> E2BIG or some such?
>
Right. That's better than -1.
> > +
> > + /* Clear all banks to avoid flushing unwanted CPUs */
> > + for ( vcpu_bank = 0; vcpu_bank <= max_banks; vcpu_bank++ )
> > + vpset->bank_contents[vcpu_bank] = 0;
> > +
> > + vpset->valid_bank_mask = 0;
> > +
> > + for_each_cpu ( cpu, mask )
> > + {
> > + int vcpu = hv_vp_index(cpu);
>
> unsigned int or uint32_t (which is the tyupe that hv_vp_index
> returns).
>
> Thanks, Roger.
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