Prev: [tip:x86/irq] x86: apic: Fix mismerge, add arch_probe_nr_irqs() again
Next: KVM: SVM: Use svm_msrpm_offset in nested_svm_exit_handled_msr
From: Joerg Roedel on 26 Feb 2010 05:30
On Fri, Feb 26, 2010 at 12:20:10PM +0200, Avi Kivity wrote:
> On 02/25/2010 07:15 PM, Joerg Roedel wrote:
> >The algorithm to find the offset in the msrpm for a given
> >msr is needed at other places too. Move that logic to its
> >own function.
> >
> > #define MAX_INST_SIZE 15
> >
> >@@ -417,23 +439,22 @@ err_1:
> > static void set_msr_interception(u32 *msrpm, unsigned msr,
> > int read, int write)
> > {
> >- int i;
> >+ u8 bit_read, bit_write;
> >+ unsigned long tmp;
> >+ u32 offset;
> >
> >- for (i = 0; i< NUM_MSR_MAPS; i++) {
> >- if (msr>= msrpm_ranges[i]&&
> >- msr< msrpm_ranges[i] + MSRS_IN_RANGE) {
> >- u32 msr_offset = (i * MSRS_IN_RANGE + msr -
> >- msrpm_ranges[i]) * 2;
> >-
> >- u32 *base = msrpm + (msr_offset / 32);
> >- u32 msr_shift = msr_offset % 32;
> >- u32 mask = ((write) ? 0 : 2) | ((read) ? 0 : 1);
> >- *base = (*base& ~(0x3<< msr_shift)) |
> >- (mask<< msr_shift);
> >- return;
> >- }
> >- }
> >- BUG();
> >+ offset = svm_msrpm_offset(msr);
> >+ bit_read = 2 * (msr& 0x0f);
> >+ bit_write = 2 * (msr& 0x0f) + 1;
> >+
> >+ BUG_ON(offset == MSR_INVALID);
> >+
> >+ tmp = msrpm[offset];
> >+
> >+ read ? clear_bit(bit_read,&tmp) : set_bit(bit_read,&tmp);
> >+ write ? clear_bit(bit_write,&tmp) : set_bit(bit_write,&tmp);
> >+
> >+ msrpm[offset] = tmp;
> > }
>
> This can fault - set_bit() accesses an unsigned long, which can be 8
> bytes, while offset can point into the last u32 of msrpm. So this
> needs either to revert to u32 shift/mask ops or msrpm be changed to
> a ulong array (actually better, since bitmaps in general are defined
> as arrays of ulongs).

Ah true, I will fix that. Thanks.

> btw, the op-level ternary expression is terrible, relying solely on
> *_bit()'s side effects. Please convert to an ordinary if.
>
> btw2, use __set_bit() which atomic operation is not needed.

Right, will switch to __set_bit and __clear_bit.

Joerg


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 | 
Pages: 1
Prev: [tip:x86/irq] x86: apic: Fix mismerge, add arch_probe_nr_irqs() again
Next: KVM: SVM: Use svm_msrpm_offset in nested_svm_exit_handled_msr