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Re: [PATCH] spapr: Rework hash<->radix transitions at CAS
From: |
David Gibson |
Subject: |
Re: [PATCH] spapr: Rework hash<->radix transitions at CAS |
Date: |
Fri, 14 Feb 2020 09:28:35 +1100 |
On Thu, Feb 13, 2020 at 04:38:38PM +0100, Greg Kurz wrote:
> Until the CAS negotiation is over, an HPT can be allocated on three
> different paths:
>
> 1) during machine reset if the host doesn't support radix,
>
> 2) during CAS if the guest wants hash and doesn't support HPT resizing,
> in which case we pre-emptively resize the HPT to accomodate maxram,
>
> 3) during CAS if no CAS reboot was requested, the guest wants hash but
> we're currently configured for radix.
>
> Depending on the various combinations of host or guest MMU support,
> HPT resizing guest support and the possibility of a CAS reboot, it
> is quite hard to know which of these allocates the HPT that will
> be ultimately used by the guest that wants to do hash. Also, some of
> them have bugs:
>
> - 2) calls spapr_reallocate_hpt() instead of spapr_setup_hpt_and_vrma()
> and thus doesn't update the VRMA size, even though we've just extended
> the HPT. Not sure what issues this can cause,
>
> - 3) doesn't check for HPT resizing support and will always allocate a
> small HPT based on the initial RAM size. This caps the total amount of
> RAM the guest can see, especially if maxram is much higher than the
> initial ram.
>
> We only support guests that do CAS and we already assume that the HPT
> isn't being used when we do the pre-emptive resizing at CAS. It thus
> seems reasonable to only allocate the HPT at the end of CAS, when no
> CAS reboot was requested.
>
> Consolidate the logic so that we only create the HPT during 3), ie.
> when we're done with the CAS reboot cycles, and ensure HPT resizing
> is taken into account. This fixes the radix->hash transition for
> all cases.
Uh.. I'm pretty sure this can't work for KVM on a POWER8 host. We
need the HPT at all times there, or there's nowhere to put VRMA
entries, so we can't run even in real mode.
> The guest can theoretically call CAS several times, without a CAS
> reboot in between. Linux guests don't do that, but better safe than
> sorry, let's ensure we can also handle the symmetrical hash->radix
> transition correctly: free the HPT and set the GR bit in PATE.
> An helper is introduced for the latter since this is already what
> we do during machine reset when going for radix.
>
> As a bonus, this removes one user of spapr->cas_reboot, which we
> want to get rid of in the future.
>
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> hw/ppc/spapr.c | 25 +++++++++++++++-----
> hw/ppc/spapr_hcall.c | 59
> ++++++++++++++++++++----------------------------
> include/hw/ppc/spapr.h | 1 +
> 3 files changed, 44 insertions(+), 41 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 828e2cc1359a..88bc0e4e3ca1 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1573,9 +1573,19 @@ void spapr_setup_hpt_and_vrma(SpaprMachineState *spapr)
> {
> int hpt_shift;
>
> + /*
> + * HPT resizing is a bit of a special case, because when enabled
> + * we assume an HPT guest will support it until it says it
> + * doesn't, instead of assuming it won't support it until it says
> + * it does. Strictly speaking that approach could break for
> + * guests which don't make a CAS call, but those are so old we
> + * don't care about them. Without that assumption we'd have to
> + * make at least a temporary allocation of an HPT sized for max
> + * memory, which could be impossibly difficult under KVM HV if
> + * maxram is large.
> + */
> if ((spapr->resize_hpt == SPAPR_RESIZE_HPT_DISABLED)
> - || (spapr->cas_reboot
> - && !spapr_ovec_test(spapr->ov5_cas, OV5_HPT_RESIZE))) {
> + || !spapr_ovec_test(spapr->ov5_cas, OV5_HPT_RESIZE)) {
> hpt_shift = spapr_hpt_shift_for_ramsize(MACHINE(spapr)->maxram_size);
> } else {
> uint64_t current_ram_size;
> @@ -1604,6 +1614,12 @@ static int spapr_reset_drcs(Object *child, void
> *opaque)
> return 0;
> }
>
> +void spapr_reset_patb_entry(SpaprMachineState *spapr)
> +{
> + spapr->patb_entry = PATE1_GR;
> + spapr_set_all_lpcrs(LPCR_HR | LPCR_UPRT, LPCR_HR | LPCR_UPRT);
> +}
> +
> static void spapr_machine_reset(MachineState *machine)
> {
> SpaprMachineState *spapr = SPAPR_MACHINE(machine);
> @@ -1624,10 +1640,7 @@ static void spapr_machine_reset(MachineState *machine)
> * without a HPT because KVM will start them in radix mode.
> * Set the GR bit in PATE so that we know there is no HPT.
> */
> - spapr->patb_entry = PATE1_GR;
> - spapr_set_all_lpcrs(LPCR_HR | LPCR_UPRT, LPCR_HR | LPCR_UPRT);
> - } else {
> - spapr_setup_hpt_and_vrma(spapr);
> + spapr_reset_patb_entry(spapr);
> }
>
> qemu_devices_reset();
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index b8bb66b5c0d4..57ddf0fa6d05 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1677,6 +1677,7 @@ static target_ulong
> h_client_architecture_support(PowerPCCPU *cpu,
> bool raw_mode_supported = false;
> bool guest_xive;
> CPUState *cs;
> + int maxshift = spapr_hpt_shift_for_ramsize(MACHINE(spapr)->maxram_size);
>
> /* CAS is supposed to be called early when only the boot vCPU is active.
> */
> CPU_FOREACH(cs) {
> @@ -1739,36 +1740,6 @@ static target_ulong
> h_client_architecture_support(PowerPCCPU *cpu,
>
> guest_xive = spapr_ovec_test(ov5_guest, OV5_XIVE_EXPLOIT);
>
> - /*
> - * HPT resizing is a bit of a special case, because when enabled
> - * we assume an HPT guest will support it until it says it
> - * doesn't, instead of assuming it won't support it until it says
> - * it does. Strictly speaking that approach could break for
> - * guests which don't make a CAS call, but those are so old we
> - * don't care about them. Without that assumption we'd have to
> - * make at least a temporary allocation of an HPT sized for max
> - * memory, which could be impossibly difficult under KVM HV if
> - * maxram is large.
> - */
> - if (!guest_radix && !spapr_ovec_test(ov5_guest, OV5_HPT_RESIZE)) {
> - int maxshift =
> spapr_hpt_shift_for_ramsize(MACHINE(spapr)->maxram_size);
> -
> - if (spapr->resize_hpt == SPAPR_RESIZE_HPT_REQUIRED) {
> - error_report(
> - "h_client_architecture_support: Guest doesn't support HPT
> resizing, but resize-hpt=required");
> - exit(1);
> - }
> -
> - if (spapr->htab_shift < maxshift) {
> - /* Guest doesn't know about HPT resizing, so we
> - * pre-emptively resize for the maximum permitted RAM. At
> - * the point this is called, nothing should have been
> - * entered into the existing HPT */
> - spapr_reallocate_hpt(spapr, maxshift, &error_fatal);
> - push_sregs_to_kvm_pr(spapr);
> - }
> - }
> -
> /* NOTE: there are actually a number of ov5 bits where input from the
> * guest is always zero, and the platform/QEMU enables them independently
> * of guest input. To model these properly we'd want some sort of mask,
> @@ -1806,6 +1777,12 @@ static target_ulong
> h_client_architecture_support(PowerPCCPU *cpu,
> error_report("Guest requested unavailable MMU mode (hash).");
> exit(EXIT_FAILURE);
> }
> + if (spapr->resize_hpt == SPAPR_RESIZE_HPT_REQUIRED &&
> + !spapr_ovec_test(ov5_guest, OV5_HPT_RESIZE)) {
> + error_report(
> + "h_client_architecture_support: Guest doesn't support HPT
> resizing, but resize-hpt=required");
> + exit(1);
> + }
> }
> spapr->cas_pre_isa3_guest = !spapr_ovec_test(ov1_guest, OV1_PPC_3_00);
> spapr_ovec_cleanup(ov1_guest);
> @@ -1838,11 +1815,23 @@ static target_ulong
> h_client_architecture_support(PowerPCCPU *cpu,
> void *fdt;
> SpaprDeviceTreeUpdateHeader hdr = { .version_id = 1 };
>
> - /* If spapr_machine_reset() did not set up a HPT but one is necessary
> - * (because the guest isn't going to use radix) then set it up here.
> */
> - if ((spapr->patb_entry & PATE1_GR) && !guest_radix) {
> - /* legacy hash or new hash: */
> - spapr_setup_hpt_and_vrma(spapr);
> + if (!guest_radix) {
> + /*
> + * Either spapr_machine_reset() did not set up a HPT but one
> + * is necessary (because the guest isn't going to use radix),
> + * or the guest doesn't know about HPT resizing and we need to
> + * pre-emptively resize for the maximum permitted RAM. Set it
> + * up here. At the point this is called, nothing should have
> + * been entered into the existing HPT.
> + */
> + if (spapr->patb_entry & PATE1_GR || spapr->htab_shift <
> maxshift) {
> + /* legacy hash or new hash: */
> + spapr_setup_hpt_and_vrma(spapr);
> + push_sregs_to_kvm_pr(spapr);
> + }
> + } else {
> + spapr_free_hpt(spapr);
> + spapr_reset_patb_entry(spapr);
> }
>
> if (fdt_bufsize < sizeof(hdr)) {
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 09110961a589..9d88b5596481 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -919,4 +919,5 @@ void spapr_check_pagesize(SpaprMachineState *spapr,
> hwaddr pagesize,
>
> void spapr_set_all_lpcrs(target_ulong value, target_ulong mask);
> hwaddr spapr_get_rtas_addr(void);
> +void spapr_reset_patb_entry(SpaprMachineState *spapr);
> #endif /* HW_SPAPR_H */
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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