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powerpc/64s/interrupt: Check and fix srr_valid without crashing 

The PPC_RFI_SRR_DEBUG check added by patch "powerpc/64s: avoid reloading
(H)SRR registers if they are still valid" has a few deficiencies. It
does not fix the actual problem, it's not enabled by default, and it
causes a program check interrupt which can cause more difficulties.

However there are a lot of paths which may clobber SRRs or change return
regs, and difficult to have a high confidence that all paths are covered
without wider testing.

Add a relatively low overhead always-enabled check that catches most
such cases, reports once, and fixes it so the kernel can continue.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Rebase, use switch & INT names, squash in race fix from Nick]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2021-06-22 22:16:28 +10:00 committed by Michael Ellerman
parent ae58b1c645
commit 6eaaf9de35
1 changed files with 89 additions and 0 deletions
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89
arch/powerpc/kernel/interrupt.c
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@ -3,6 +3,7 @@
#include <linux/context_tracking.h>
#include <linux/err.h>
#include <linux/compat.h>
#include <linux/sched/debug.h> /* for show_regs */
#include <asm/asm-prototypes.h>
#include <asm/kup.h>
@ -215,6 +216,88 @@ static notrace void booke_load_dbcr0(void)
#endif
}
static void check_return_regs_valid(struct pt_regs *regs)
{
#ifdef CONFIG_PPC_BOOK3S_64
unsigned long trap, srr0, srr1;
static bool warned;
u8 *validp;
char *h;
if (regs->trap == 0x3000)
return;
trap = regs->trap;
// EE in HV mode sets HSRRs like 0xea0
if (cpu_has_feature(CPU_FTR_HVMODE) && trap == 0x500)
trap = 0xea0;
switch (trap) {
case 0x980:
case INTERRUPT_H_DATA_STORAGE:
case 0xe20:
case 0xe40:
case INTERRUPT_HMI:
case 0xe80:
case 0xea0:
case INTERRUPT_H_FAC_UNAVAIL:
case 0x1200:
case 0x1500:
case 0x1600:
case 0x1800:
validp = &local_paca->hsrr_valid;
if (!*validp)
return;
srr0 = mfspr(SPRN_HSRR0);
srr1 = mfspr(SPRN_HSRR1);
h = "H";
break;
default:
validp = &local_paca->srr_valid;
if (!*validp)
return;
srr0 = mfspr(SPRN_SRR0);
srr1 = mfspr(SPRN_SRR1);
h = "";
break;
}
if (srr0 == regs->nip && srr1 == regs->msr)
return;
/*
* A NMI / soft-NMI interrupt may have come in after we found
* srr_valid and before the SRRs are loaded. The interrupt then
* comes in and clobbers SRRs and clears srr_valid. Then we load
* the SRRs here and test them above and find they don't match.
*
* Test validity again after that, to catch such false positives.
*
* This test in general will have some window for false negatives
* and may not catch and fix all such cases if an NMI comes in
* later and clobbers SRRs without clearing srr_valid, but hopefully
* such things will get caught most of the time, statistically
* enough to be able to get a warning out.
*/
barrier();
if (!*validp)
return;
if (!warned) {
warned = true;
printk("%sSRR0 was: %lx should be: %lx\n", h, srr0, regs->nip);
printk("%sSRR1 was: %lx should be: %lx\n", h, srr1, regs->msr);
show_regs(regs);
}
*validp = 0; /* fixup */
#endif
}
static notrace unsigned long
interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
{
@ -264,6 +347,8 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
}
}
check_return_regs_valid(regs);
user_enter_irqoff();
if (!prep_irq_for_enabled_exit(true)) {
user_exit_irqoff();
@ -440,6 +525,8 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
}
}
check_return_regs_valid(regs);
/*
* Stack store exit can't be restarted because the interrupt
* stack frame might have been clobbered.
@ -469,6 +556,8 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
local_paca->irq_happened &= ~PACA_IRQ_HARD_DIS;
} else {
check_return_regs_valid(regs);
if (unlikely(stack_store))
__hard_EE_RI_disable();
/*